You can restore you system earlier date, if you have xp go to control panel or accessories. Not sure it will take the viruses off.

If you go frys.com you may get free after mail in rebate virsus software, or if you are a student  you will get free virus software get it and do a full scan.

If not save your important documents and reformat, if it is a desktop , someone suggested me that there is a battery on motherboard take is out for a while ( i do not know the reason but suggesting every one).