New power supply and video card, computer not starting.

[ErikEngle]

I upgraded my power supply from a 400w to a 750w and changed nVidea 8800 to a Radeon 4850. Before my computer was running fine and now it will not start. It turns on, all the fans are spinning, the dvd drive opens and reads, and all the lights on the case are coming up as normal, but the moniter shows No Signal then goes into its standby mode. I have tried every connection between computer and monitor with numerous cables having no diference, and have tried a second monitor. I tried putting the old video card back in with the power supply and it did same results, nothing at all coming up on screen, so I'm assuming that I did something wrong with the power supply. I connected the 4 pin and 24 pin to the motherboard and the 6 pin to the video card and double checked them.

750w diablotek phd 750
Radeon HD 4850 1g

Any advice would be appreciated.

 

[o1die]

I would run the 4850 with the 400w power supply and return the 750, or rma it to the manufacturer. The 4850 requires about the same power as your old 8800gt, so you should be ok.

 

[ErikEngle]

I just rehooked up my old power supply and tried it with both cards, and I cannot get either of them to work as well. I must have moved something or accidently knocked a wire or something loose?

 

[jsc]

I just rehooked up my old power supply and tried it with both cards, and I cannot get either of them to work as well. I must have moved something or accidently knocked a wire or something loose?

Most likely. Much less likely, but still possible, is that something else failed during the upgrade process.

It sounds like you replaced both parts at the same time. Mistake. You should have replaced each part separately starting with the PSU and tested after each step. Hindsight, right?

First thing now is to get the original system working. Our standard checklist and troubleshooting thread:
http://www.tomshardware.com/forum/261145-31-read-posting-boot-problems

Try to verify (as well as you can) that the PSU works. If you have a multimeter, you can do a rough checkout of a PSU using the "paper clip trick". You plug the bare PSU into the wall. Insert a paper clip into the green wire pin and one of the black wire pins beside it momentarily - "momentarily" being defined as less that one second. That's how the case power switch works. It applies a ground to the green wire. Turn on the PSU and the fan should spin up. If it doesn't, the PSU is dead.

If you have a multimeter, you can check all the outputs. Yellow wires should be 12 volts, red 5 volts, orange 3.3 volts, blue wire -12 volts, purple wire is the always on 5 volt standby line. The tolerances should be +/- 5%. If not, the PSU is bad.

The gray wire is really important. It sends a control signal called something like "PowerOK" from the PSU to the motherboard. It should go from 0 volts to about 5 volts within a half second of pressing the case power switch. If you do not have this signal, your computer will not boot.

Unfortunately (yes, there's a "gotcha"), passing all the above does not mean that the PSU is good. It's not being tested under any kind of load. But if the fan doesn't turn on, the PSU is most likely dead.

On to the real troubleshooting ...

Disconnect everything from the motherboard except the CPU and HSF, the two power cables going to the motherboard, and the case power switch. Boot. You should hear a series of long single beeps indicating missing memory. Silence here indicates, in probable order, a bad PSU, motherboard, or CPU - or a bad installation where something is shorting and
shutting down the PSU.

If you get the long beeps, add a stick of RAM. Boot. The beep pattern should change to one long and two or three short beeps. Silence indicates that the RAM is shorting out the PSU (very rare). Long single beeps indicates that the BIOS does not recognize the presence of the RAM.

If you get the one long and two or three short beeps, test the rest of the RAM. If good, install the video card and any needed power cables and plug in the monitor. If the video card is good, the system should successfully POST (one short beep, usually) and you will see the boot screen and messages.

Note - an inadequate PSU will cause a failure here or any step later.
Note - you do not need drives or a keyboard to successfully POST (generally a single short beep).
Note - the beep patterns I mentioned seem to be the most common. Those are what I get with my eVGA 680i motherboard, my three Intel Gigabyte boards, and my old AMD AOpen board. Other board may be different.

If you successfully POST, start plugging in the rest of the components, one at a time.

 

[ErikEngle]

If you get the long beeps, add a stick of RAM. Boot. The beep pattern should change to one long and two or three short beeps. Silence indicates that the RAM is shorting out the PSU (very rare). Long single beeps indicates that the BIOS does not recognize the presence of the RAM.

I'm getting silence for this part, when I put in a stick of RAM. I tried 4 sticks and silence, but the computer was working fine before I put in PSU/Vid card and I don't think I got near the RAM when I did it. Either way what would be the next step?

 

[o1die]

If you can't get either video card to work with one of the power supplies, then I would request an rma from the motherboard manufacturer's website. It takes about one day to process an rma request. Some don't even require a copy of the receipt, just the board serial number, usually written in white id lettering somewhere on the board or the box it came in. It takes about 2-3 weeks to get another board back. Newegg has some socket 775 low end boards in their open box section with onboard video which may hold you over if you don't have a spare pc. You'll have to check the specs carefully before ordering. They're around $20 with shipping, if they have any left.