Blaster virus or not?

Ok so i have a problem with my computer, everytime I try to turn it on...it will get to the windows loading part and then restart itself...I thought it was the motherboard, but i found out when I put the harddrive into another computer it acted the same way. What is this problem and how can i fix it?...I cant run an antivirus or dl a patch to the computer because i cant even log in to my desktop...PLease help!