Hai Friend
I think you have done almost all tests. I think problem may be in your
power supply unit. Are you using UPS?
Still I will give some suggestions. Once check with Prevx1 anti
malware software. It is a powerful anti-malware software.You can
download it from the following site.
http://www.prevx.com/security.asp
If the above not works,then first scan the system with Bit Defender
Antivirus Plus then with Avira AntiVir PersonalEdition Classic.
Before
using these softwares you have to uninstall your AVG antivirus.If
these softwares find any virus affected files remove them. But
becareful some programs may not work if you remove some virus
affected
files. So I will suggest you to read completely the article below on
Viruses then do experiment on your computer.
The article is:
http://technodata.blogspot.com/2007/...s-glowing.html
So after the above tests you will come to a conclusion whether your
computer is affected by any virus.
If you come to a conclusion that your computer is not affected by
virus then do like this.
Freshly format your harddisk and reinstall Win XP Pro with service
pack2. Even then your computer giving problem then you can come to a
conclusion that it is completely hardware problem. Then by trial and
error you can find which hardware component is giving problem? O.K.
Don't think that I am testing your patience.