tried this. http://www.avast.com/en-eu/uninstall-utility

did you remove old AV before installing avast? http://www.avast.com/en-eu/faq.php?article=AVKB11

could have a virus too... not sure).
if you want a check follow instructions and attach requested logs. http://forum.avast.com/index.php?topic=53253.0

we need Malwarebytes / OTL / aswMBR logs