|you probably didn't uninstall the previous expired anti-virus from your PC properly, so that would cause lots of problems when trying AVG.|
You most likely have an unwanted rootkit installed...it is quite easy to remove at most times.
Doenload and run these 3 progs in EXACTLY the order listed and DO NOT reboot untill after the last scan has finished running.
2- tdss killer
If the above doesn't clear it out...do the SAME, ONLY this time in safemode.
Some HELP in posting on Computing.net plus free progs and instructions 7 Golds