PSU's and Graphics Cards Gone Crazy

I have a very unusual problem I'm hoping someone here can help with. I'm trying to get an EVGA 8800 GT video card installed in a Dell Optiplex 755. The PSU that comes with that is only 280w so of course I figured I'd need a new one. I also borrowed a gateway PC with a standard factory installed 300w PSU and a separate nvidia 520 GT video card for testing - you'll see why in a moment. So here are the results of the tests:

1) Gateway PC that I borrowed from a friend with a 300w original PSU + 8800 video card works fine. Or at least, it boots up fine, he didn't have any games installed to test/play and I didn't want to push the card with a 300w and mess up his PC. So, this means that the 8800 card is ok, or at the very least, the card isn't *completely* broken. Check.

2) Dell PC with 450w Diablotek PSU OR brand new 600w Ultra PSU + 520GT video card works fine. So both of these PSU's are ok, or at the very least, not completely broken. Check.

3) Dell PC with 450w Diablotek PSU OR brand new 600w Ultra PSU + 8800 GT video card does not work. Not only will it not boot, and doesn't send any signal to the monitor, the PC constantly powers up and down by itself and doesn't stop until I disconnect the power.

What?! This makes no sense. The only possibility I can see that reconciles 1-3 above is that both the 450w and 600w PSU's have less power output than the generic factory installed 300w. But that doesn't add up either. Its not like I was trying to run intense applications on them, they wouldn't even boot. Yes, they are both cheapo PSU's - so is the gateway generic one that seems to run the card fine. Also, the 600w one is rated at over 45A on the 12v line.

At this point I'm completely out of ideas and going to have to chalk it up to evil computer ghosts. Can anyone help me or suggest a next step?
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  1. I'm assuming your secondary power connectors were plugged in? I can't imagine a 300watt psu even having any. Strange that it booted up but the more powerful psu's didn't.
  2. @egilbe - Yes, in all cases the 8800 had the 6-pin extra power plugged in. The gateway with the 300w factory PSU had a 6-pin as well. The 520 has no 6-pin connection so of course wasn't ever plugged in there.

    I've been racking my brains trying to come up with other possible things to check/test/change but I've got nothing. I thought maybe I need to uninstall the nvidia drivers for the 520 before connecting the 8800, but no, that definately shouldn't cause it not to send any monitor signal and power up/down constantly. Maybe a Dell Optiplex 755 simply cannot use a 8800 card? Google gave no mention of any similar issue.

    If anyone else has any thoughts or if I can provide any other information please let me know.
  3. Do you know if the computer boots into Windows at all? And just not displaying sound? (ie the Windows welcome sound) I've had a case like that where the DVI port on a friend's 5450 was bad, so I had to use VGA. Worked like a charm when we tried that :)

    Actually I just re-read your post...I've had a long day so I'm sorry I read it wrong :( I know that what I posted is of no use :lol:
  4. could be two issues....on the 8800 could be pulling more power then the dell mb can handel on the pci slots. tht why there a 6 pin connector on it. the other issue would be that the dell ps has more then one power rail and the rail that it on is over loaded.
    most older ps or low wattage ones will have only one rail. for 12v. the 520 card as it newer needs less power then the 520.
    105 WM 8800
    30w for the 520
    so it could be the mb or the ps not holding up the 8800
  5. +1 on the power going to the PCI-E slot going flonky.
    the 520 will draw 1/3 the power of the 8800.
    try cleaning the slot and pitch that time bomb call a diablotek PSU!
  6. First, an update: Connecting a 7900 GS video card (which uses a 6-pin and more power than the 520, but less than the 8800) to the Dell + 600w Ultra PSU works fine.

    I also tried connecting the 8800 to the dell + 600W ultra psu, but NOT connecting the 6-pin connector to the graphics card. Instead, I connected the PSU from the gateway to the 6-pin. In other words, the 600w PSU was running the Dell, but the 300w gateway psu was feeding the 6-pin, so I had 2 PSU's at once going into 1 PC. This actually *stopped* the problem of the PC just constantly powering up and down, and I could tell it was actually booting in the background based on the sounds, but I still got no monitor output! Very, very confusing.

    @smorizio and looniam - Thanks for the replies, not quite sure I understand the suggestions though. None of my PSU's have more than one 12v rail, although they all have different Amp ratings on that rail. The 600w psu has a 40+ 12v amp rating though. In any case, are you two saying that the PSU might be fine, and giving plenty of power, and the 8800 card might be fine, but the motherboard slot itself is bad? Well, not bad, because it runs the 520 and 7900 fine, but very slightly damaged somehow so its not giving full power or something?
  7. Also, I thought of 1 other thing I could try but I want to get feedback on it first before I spend hours doing it. What if I connect the 8800 + the 600w psu to the gateway machine? If it works, would that mean that the motherboard/PCI-slot on the Dell is 100% definately the problem? And if it doesn't work, would that 100% mean that somehow the 600w psu isn't enough for the 8800? Thanks.

  8. so far you have proven a card that draws more than 75 watts, the power supplied by pci 1.0, slot fails regardless of what psu is used.

    doesn't THAT tell you something?
  9. Once again looniam, appreciate the reply, but I don't have any idea what you mean I'm afraid. I can't tell if you are asking me a riddle or a trick question or what. Set it to EZmode for me and make is simple like (hypothetical):

    A) Your tests show that the mobo/PCI slot is very slightly damaged, still completely functional but not delivering full power.

    B) Your tests show that your 600w PSU isn't delivering enough power to the 8800 card and so you need a better/higher power PSU.

    C) Your tests show that the video card is slightly damaged, still functional under some circumstances but somehow not under others.

    D) You have a bad case of Computer Ghosts.

    E) ???
  10. Update: So I connected the 8800 video card, and the 600w PSU to the gateway PC (instead of the dell optiplex 755), and it booted fine. This seems to narrow the problem down to the dell motherboard and/or PCI-E slot. What is still confusing is that the dell runs the 520 GT and 7900 GS cards fine, so the mobo/pci aren't broken. Also, the gateway PCI-E slot is 1.0, just like the Dell so its not a 2.0 vs 1.0 issue.

    Is it possible that the PCI-E slot on the dell is damaged in such as specific and tiny way that it is fully functional, delivering power, but delivering slightly less power than it should be? That seems very, very odd. But I can't think of any other explanations.

    Anyone have any thoughts, tips for fixes or things I might try? I can't afford to replace the whole mobo.
  11. i like answer A! :)

    clean the first 4 sets of pins on each side of the slot, the 12 volts supplied and the grounds.
    here is a pin out of a x16 slot (down the page a little)

    it does appear that either one or two of the pins are delivering power.

    if cleaning does no good than a connection in the PCB is faulty. not much can be done then.
  12. Well cleaning didn't seem to help unfortunately. So now unless someone else has another suggestion for how I might get it working, I have to pick between the following 2 setups:

    2.33ghz core 2 duo + 520 GT 1GB video card
    1.86ghz core 2 duo + 8800 GT 512 MB video card

    Which would be better for gaming?

    Also, how is it that I always get the ridiculously rare/specific/unusual PC problems? Its not like a bad video card, or a bad PSU, or a bad mobo, or a bad slot. No, for me it has to be a 90% working slot that gives power, but not *quite* enough power... /sigh
  13. 2.33 ghz core 2 duo and the 8800gt, probably. Neither is "really" that good...6 of one, half a dozen of the other
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