how to cure your hard disk from continuous rebooting

i had a problem
displaying , "your task manager is disabled by administrator !!"
i was surprised to see , that i had seen these in almost 87.56% of cyber cafes i visited !! (pun xtended )
but now as i had net @ my home , n i m only on pc n i m only admin , how come ??
then i googled a lot only to find that it is a virus !!!
even my antivirus did not found it !!
i faced problem that every time i rebooted my pc , just message would come showing options as
1. restart in safe mode
2. till last good configuration
3. in ms prompt
but trying all , my comp used to get restart restart and restart
if yours not a virus , then open cpu , remove and place again RAM as sometimes , it could lead to this problem !! if then also not , it is good thjat you have backed up your data , as it is aiming to crash ,m maybe , already crashed !!
always use better antivirus !!!