You don't say what, if any, antivirus programm you use, or ried to use..
I propose to use AVG, Avira or Microsoft Security Essential.
All are available fro FREE.
For AVG, go to: free.avg.com
Install one to run in the background. If you install more than one, the second MUST be set to only run manualy. That is, Only when you explicitely start it.
Electro, April 2011