Deleting from system and no virus found.

1) a bad harddrive will cause this to happen!
right click 'my computer' >explore > r. clk 'c'drive of local drive brings up properties > select tools tab > choose eror checking and reboot to allow the system to check your harddrive for errors. If there are lots of errors the system may be able to repair them but i would start looking for a new replacement harddrive.
2) you ran an anti-virus program and found nothing...try another program and see what it finds:
AVG Free Advisor - Free antivirus and anti-spyware downloads
Free antivirus - avast! 4 Home Edition
Free antivirus - Avira AntiVir (what I use)

3) it may also be caused by a consotium of malware/spyware. So look for a good anti-spyware/malware programs
PC World - Our Favorite, Free Anti-Spyware Programs for some good choices

Keep us posted!