xp hangs at welcome screen

[giney]

two days ago the computer restarted(as if someone removed the power cord) itself while working and then it hangs at the win xp splash screen. i thought this a software problem and tried many ways(like scanning the pc) and ultimately thought of reinstalling xp as the problem persisted. but while installing xp the computer hangs every time at the "Volume License Number" windows where we have to enter product key. finally i changed the the partition c:\ to d:\ and it got installed. but now it hangs most of the time at welcome screen and if by chance you see the desktop the after one minute or so the computer again shuts itself (like removing power cord) directly.

i tried running live CD of Ubuntu 10.4 but it also hangs after showing the desktop. everything hangs after 1 or 2 minutes even if you don't do anything.

the caps lock key and scroll lock key keeps blinking after ubuntu(live cd) hangs but not in xp.xp directly shuts itself or hangs at welcome screen.

it even hangs in safe mode

i know it is not the problem of overheating because i have applied new coolant paste and two fans are there.

the memory is also not faulty as i have checked in another computer.

i have two harddisk ( 40 gb and 80 gb) whose status is "healthy" as shown in DiskUtility of Ubuntu.

My system Configuration is:

Win XP SP2
1 GB DDR RAM
120 Gb (40 + 80) Harddisk
intel i845 motherboard
Samsung DVD writer
300 W PSU

please help me. my school project is on this computer and i dont wont to format my other partitions (except c:\ and d:\)

[Sam]

looks like your PSU as well as HDD are faulty. either one of them or both. try get it check in a friends PC 9the Hard drives). the PSU is way too low @ 300W.

[giney]

checked hard disk with hdd re generator. no bad sectors found.

i cant tell anything for PSU

[ico]

What all PCI devices are you using?

[giney]

there are no PCI devices.
only hard disk,ram,dvd writer,Psu,PS/2 mouse and keyboard.
nothing else

[ico]

If Ubuntu Live CD hangs, I don't think there is any problem in the Hard Disk.

Try changing your RAM.

[giney]

checked ram with memtest86+ and windows memory diagnostics. no errors shown.

i have two ram and and i took out one and used other and vice versa . no difference in the situation.
i am able to boot using hirens boot cd 10.0 without any hangs.
it hangs in xp or any thing else usually after the splash screen without showing the welcome screen.
no graphic drivers installed. not able to boot in vga mode also.
it just does not show damn graphics.

[asingh]

Please update your signature, it is quite painful to browse to the top to understand your signature.

Re-do all the connections again. Which PSU you have.