Help please...computer won't boot

[shadyb1]

Okay, I've decided to pick the brains of the TechIMO masters...

I'm attempting to diagnose a computer problem for a friend. The system is as follows:

Dell Demension 4550
P4 2.6
512 Mb DDR RAM 333MHZ
60GB HD
Radeon 9700 pro
Soundblaster Live
CDRW
DVDROM
Modem

The computer shuts down during boot like clockwork. The furthest I've been able to get is the Windows XP boot screen (but that was only once). Usually it just shuts down about 3-10 seconds after posting. Sometimes if I'm lucky, I can get into the BIOS before it shuts down. There, of course, is no hardware monitoring within the Dell BIOS, so I can't tell if something's overheating. Everything in the BIOS looks good, though, and I'm not getting any error messages throughout the process.

Here's what I've done so far (nothing's worked):

-disconnected everything except memory, CPU, and video card
-switched out the power supply
-switched out video cards (replaced with old Geforce2 TI - it wouldn't post at all after I did that)
-switched out memory
-checked and reseated all connections
-cleared CMOS

Nothing helped.

I noticed after taking off the heatsink that there is a thermal pad on the bottom, but there is only the shiny part which is touching the CPU - there wasn't any melted thermal material, just the reflective part of the pad. I put some Arctic Silver 5 in between, but it didn't help.

Any suggestions? I'm guessing that either CPU or motherboard is defective? What does everyone think?

Thanks...

[watchtower7]

you must test the memory.
memtest 86 seems to be best.
unfortunately, the only thing you didn't check is the usual problem.

[The Real Bingo]

He said he switched out the memory, so that shouldnt be the problem. If you have a spare processor laying around maybe you can try that to narrow it down to the mobo.

[shadyb1]

I switched out the memory module for another one known to be good and being used in another system. I also tried both dimm slots - didn't help.

[watchtower7]

I had a bad mobo once...when I ran memtest, it showed the memory was bad but I new the memory was good in another system so the mobo became the culprit. And was guilty as charged.

[shadyb1]

Okay...I switched out the 2.6 P4 with a 2.0 P4...I was able to get to the Windows boot screen and then it shut down again. I put the 2.0 back in the other system and it works fine.

So it's probably not the CPU...I guess that leaves the motherboard as the culprit?

[elmers]

Perhaps the cpu is overclocked above its abilities. Load the failsafe bios settings.

[shadyb1]

The person who owns the computer didn't mess with the BIOS at all (they were literally afraid to unplug the monitor!) - everything's set to auto detect configuration and everything is recognized as being set at stock settings.

[elmers]

Well then you mobos prolly failed. Try the components on a different mobo if you really have the time, I guess you tried everything else...