Hi, I really hope someone can help.
I have a Dell 2350 running Xp SP2 with 512RAM chip, DVD, CD/RW, Floppy and 2 HDD.
My original problem began with the computer shutting off after startup.  There was not any new programs or hardware installed prior to the problem that I am aware of.  I have only been able to get the desktop to show 2 times since the issue began before it shuts off. The first time the sys ran long enough for me to get to the DEVICE manager, which showed no hardware problems then it shut off, and after about a hundred more tries, I was able to get in and begin running Del system diagnostics from BIOS and it ran almost 13 hrs while executing the extended version when all of a sudden it shut off, and has not displayed anything on screen again.  Therefore I cannot get back into BIOS to check boot sequence or change it because it will not stay on more han a few minutes now or show anything on the monitor.  I have tried hitting function keys after restarting with no disks in the drives to try and get to SETUP screen, no luck...., I tried replacing the motherboard with no fix (under Dell support recommendation, when it didnt fix the issue they gave me a refund), then put orig board back in and I replaced the power SUPPLY with no difference either.  Recently I replaced the CMOS battery, that did not help.  I have ruled out hardware config by unplugging everything then restarting between adding components again.  No matter what components are plugged up, sometimes it runs a few minutes sometimes only a few seconds all without video or noiss of the drives working.  I have tried booting from the install CD, and made bootable floppy's (6) for SP2 online along with a MSDOS startup disk.  All boots reslt in nothing. I see lights flashing on the drives, mouse and keyboard, but it will do nothing else.  Grrrrrrr    Video is integrated without a slot to try another graphics card.
Also tried another monitor...still nothing.  I am suspecting a virus, and planned on using the system disk to format and reinstall, but I cannot get it to recognise anything I put in.  HELP!Seems like you've checked about everything except for the memory...

Hvae you checked it as well?Your CPU could have overheated to the point of no
return.Hopefully not.

I think you NEED to clean and reseat your CPU and heatsink.

If you do ,don't forget the new thermal paste.I've saw this before with bad RAM.  Could be or could not be.  I've seen it before with PROCESSOR issues too.