Cannot boot into Safemode

Hi,

I hope someone can help me? I noticed that my computer keeps on freezing up and not responding to anything except the restart button. Also it would restart by itself for no reason.

I first suspected some malware so I ran some scans.

AVG Antivirus (found nothing)
Spybot (kept freezing up)
Ad Aware (kept freezing up)
Microsoft Anti Spyware (found nothing)
Microsoft Malicious Software Tool (found nothing)

So I tried doing an online scan.

Bitdefender (kept freezing up)
Panda ActiveScan (kept freezing up)
Windows Live Safety (kept freezing up)

So I tried to boot into safe mode and run the scans again. But when windows reaches the log in screen it just restarts. I’m hoping if I can fix this problem, everything else will be ok. I’ve searched the Microsoft Knowledge Base and found nothing.

Has anyone got any ideas?

Here is my system:

Windows XP Professional service pack 2
MSI KT3 Ultra 2R Motherboard
AMD Athlon XP 2200+
512Mb RAM
MSI NVIDIA GeForce Ti 4600
SoundBlaster Audigy 2
80Gb Hard disk
MSI DVD ROM
MSI CD RW

Numan