1. BOOT THE COMPUTER IN SAFE MODE ONLY BY TAPPING F8 ON STARTING THE COMPUTER.
TRY UNINSTALING AVAST FROM ADD/REMOVE PROGRAMS WITHIN SAFE MODE.
Min processes are running in this mode. Any other traces of previous antviruses need to be removed. Ie NORTONS/SYMANTECS / AVG'S/ MACAFEES ETC. Need to use their removal tools!.
2. Download malware bytes free and do antispyware check./ and remove what it finds and report again.