Comp Just shuts on start.Wont start up for more than 3 seconds.

Yesterday I laid down to wake up and find my computer shut off with a blinking yellow power light. Ive removed all hardware that could conflict. I have had it for over 6 months now no problem. I thought it may be my power supply so I went out and purchased a corseair 600 watt power supply. It is a dell optiplex gx280. 2 gigs ram the power supply I said and an xfx radeon 4550hd graphics. OK when I go to power it up system fan starts external fan starts. Hard drive starts. Monitor light turns green then bam it shuts off. Some starts are a little longer lasting than other times. Usually it just barely powers on then shuts off. What I described as hearing everything run then instant shut off last for about 3 to 4 seconds. I switched the cmos battery as well. ANY feed back please. I know its got to be a semi easy fix. Unless my mobo is shot. Like I said Ive stripped it down to just power and mobo and I get the same result. PLease help Thanks Josh.
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More about comp shuts start wont start seconds
  1. Did you plug the 4 pin power plug into the motherboard?
  2. Yeah :( still nothing
  3. Ive had it for about 4 to 5 months now and it worked just fine till yesterday. Then this happened.
  4. Did u check the temp of the proc after instant shutdown? if it to hot "HOT" need to reseat the heatsink. (try touching it directly)

    try using one ram no HDD, and get into bios, if it can get into bios look for anything wrong from the sensor. (also try another stick in case of some bad ram)

    if nothing work u might need get the mobo out of case in case there is some short......

    if bread boarding is not work, new mobo time.......
  5. I have done everything aside from removing the heat sink. Ill hook it up again today without the heat sink on it to see if it gets hot fast. My question is if it over heated because of the processor how do I reset that? Just remove my processor and put it back in. Also I have done everything even ram test. I do get beeps when its not in but it only stays powered for a few seconds. It even makes contact with my monitor turning it from standby to green light then everything shuts off. I have things like . well cpuid, coretemp, speedfan. None of them will pick up any of my tempratures. How do I reset my mobo or processor. Or convert back to original bios if thats a problem. Like I said before I cannot even get it to stay on long enough to go into bios or do anything. I tried adding one piece of hardware at a time. in different combinations. Like just a ram stick. Just a HD, Just my Gpu. All had the same affect. I thought it was the power supply so best buy took it back and gave me a better one. So I know its not an issue with that. Ill try the heat sink and removal of the processor like you said. Anymore info would be nice. I purchased the comp second hand. I have 2 brand new gig sticks of ram brand new sata hd. New XFX 4550 Graphics card and new corsair 600 watt supply. My socket is LGA 775 ram DDR2, PCI-E and sata HD. Is there a replacement board you may know of that would be capable of letting me switch all my new stuff to it. Id hate to have spent the few hundred dollars on all this stuff just to have it go to waste if it is a bad MOBO. Thank you very much for your help , and sorry for the long reply. Thanks Josh. oh by the way what do you mean bread boarding?
  6. Somehow I have 2 accounts on here.... I am versus_josh as well. Ill try to fix that sorry for any confusion.
  7. Do not need to remove the heatsink to check the temp when it turns on, and off unplug all the power, discharge remaining power and touch the heatsink, When u check the temp did u check/touch the NB/SB temp? (just touch the heatsink, but remember using anti static approach using anti static device or by touching large metal object like door knob, etc).

    changing heatsink could be easy or challenging depends of the heatsink model, but there lots of guide/video on internet :D ...

    Did u have onboard vga? Try turn on before it shut down press the reset button and see if it still shut down or it can get couple more sec...

    I once had vga that became to old (i'm suspecting my bad psu caused it) that it will need that trick to make my system turn on (no problem when it's on, until i'm turning it off again)

    edit: looks like dell have onboard vga, did u already try without GPU, if the same problem than GPU gone bad is out from suspect........

    If it not work, your psu are new, gpu, ram and temp is fine, I'm only can suspect mobo gone bad.....
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