Bootloading restart issue

Firstly if this is in the wrong place feel free to move it just I am fairly sure it is a hardware issue. All you might know better.

Spec:
C2D e6300 (stock: more than enough for XP 1.86GHz)
Corsair DDR2 2GB (2x 1GB sticks) 677mhz
p965 motherboard
Nvidia 7300GT
475W akasa PSU
Windows XP SP2


My issue is that when I boot up my computer in Windows XP that just before as the system is about to go onto the login screen at the end of loading bar screen it just restarts. Then on restart it says it had failed to boot correctly, and gives me the usual FUBAR options of Last known settings, Safe Mode... (I have tried all the modes it does the same thing).

I don't think it is the PSU as it restarts in the same place every time and the system turns on fine, and it manage to outlast HDD spin up (highest ampage draw)

I don't think it is the bootloader or MBR as it manages to start the boot process and load the boot process.

I don't think it is the RAM as I have tried each stick on their own and get the same result with both.

I have already tried CMOS reset although I don't see how that would affect anything, again same result.

It has been working fine for the last 2 Years.

I really do not want to lose the data on the system

Thanks for your help.