Old PC Only Working In Safe Mode!

My mother called me round to her house earlier today and said that her PC had stopped working, so when I checked it out it had the following problem which I'm hoping you guys can help me out with:

When turning the PC on it loads up to the point shown below in the screenshot...

http://www.theeasypc.co.uk/images/xpload.jpg

When it gets past there, the screen goes blank and that's it. Other times, it'll get PAST that screen to another blank screen but this time the mouse pointer will show. After a while the whole PC will just reboot and go through the same process all over again.

The only thing that actually works properly is safe mode (with networking) which I am using right now to type out this post. I went into the BIOS to see if it was anything to do with the PSU and the +12v reading was 12.22, which as far as I know is fine, although I could easily be mistaken.

Anyway, as for PC specs they are shown below (they are very old so please keep that in mind):

OS - Windows XP Pro
CPU - Intel Celeron 1.7Ghz
Video Card - Not sure, but it's very old... I do know it's 256mb though. It won't say in DXDiag or Everest.
PSU - Also an old (unbranded I "think") one.
Ram - 768mb DDR I

Anyway, although (as you can see) the above specs are outdated, the PC has been running absolutely fine up until now and all of a sudden this has happened and I've no idea why. I've run Virus checks (AVG, Ad-Aware, Spybot etc) in normal AND safe mode, yet they found nothing.

I'd really appreciate it if anybody has an idea as to what this problem could be.

Thanks a lot in advance

 

be sure your memory is ok as faulty memory can cause all sorts of problems, try this- http://www.memtest.org/

It is a good idea to check the voltage from the PSU but the 12volt rail rarely gives problems 12.2 is fine but you must check your +5volt & +3.3volt rails, if the 5volt rail is dipping below about 4.5v-4.6v all sorts of problems can happen.

 

Seems ok during safe mode means something might be loading up that's just not good.
Check to see what is loading up on startup.

Definitely follow the malware removal guide if you haven't already: http://forums.majorgeeks.com/showthread.php?t=35407

 

Also use MSconfig to remove all the start up options and if it boots then you have a list of the software causing the problem and can remove it in safe mode.

 

Thank you very much, I'll give that a go & get back to you if it doesn't work.

Much appreciated!