"Your computer is infected"

Yesterday evening I received this error message: "Your Computer is infected" at the bottom right near the clock with a cross in a red circle. I did some scan with avst software & other anti spyware software but it does nothing, and frequently a big message that opens there that I am a victim of spyware (dialog "xp center infected" + various pop-up.) All software can find no spyware. How to remove these messages? thank you in advance

Download HijackThis by searching on google & then Start HijackThis by double clicking on its icon and then click on Do a system scan only. The report is reproduced immediately after the scan in a window-type Notebook just make a copy and paste the results in the forum

in order not to lose time, when you have posted the report Get Smitfraudfix

Decompress the archive
Execute by double clicking Smitfraudfix.cmd
Seconded any key to continue
Arriving at the command prompt, enter the letter L in order to fix the switch to English
On the menu, choose Option 1: Research
Post the report generated in the forum