computer reset problem

[harsharam]

Recently my desktop started reseting randomly.  Need help diagnozing the problem.
Here is the details.

motherboard is 848P-A,
have 600W power supply.
nvdia 5200 graphics card.
3 IDE harddisks of varying capacity and 1 SATA disk.
2, 512MB DDR memory. DIMM
HP CD-RW drive.
Windows XP is installed on the SATA disk.

The machine boots up and stays up if booted in 'safe' mode.
However if booted in normal mode it resets randomly, either during the boot process or about 2 minutes after logging in.

Tried a fresh install of windows on another harddisk, but the system suddenly resets during install.
Tried booting on Fedora Core Linux, same problem, either hangs or resets.

Tried disabling each disks, changing graphics card, disabling on board devices through BIOS.
problem persists.

Did some motherboard diagnostics using multimeter and instructions provided somewhere on fixya.com(cannot locate the exact link, right now).  voltages show up right as per the instructions.

what could be going wrong?

[homer]

RAM. remove one of the two sticks and see if it randomly resets, then swap the sticks of RAM and see if it randomly resets. this will determine which stick, if either, is faulty. if the problem persists after testing each stick, then we will know the RAM is not at fault.

[ale52]

Possible flaky power supply.  Do you have another?

Alan <>< 

[harsharam]

yes. have tried removing each memory stick and then swapping them. No combination stopped the problem.

also this problem initially showed up when I had a 400W power supply. So thinking that the power supply was the culprit, I replaced it with a 600W power supply.  The problem continued even after that.

I this point I am thinking motherboard to be the culprit, since I tried installing windows XP fresh. By removing all devices, but the CD drive, and plugged in a brand new SATA disk.  But the install stopped inbetween due this random reset.   

[patio]

Is the 600W new or used ?
What brand is it ?

[harsharam]

its brand new.

cooler master extreme power duo

[ale52]

If the problem followed you after you've replace the power supply then you're motherboard is probably hosed. 

Alan <>< 

[patio]

Although i have seen brand new PSU's DOA i'm afraid Alan may be right here...