Not sure what you mean, if avast doesn't run, how do you know you have the viruses ? Can you start avast at all ? If it will start but not scan, open the menu and select "schedule boot time scan" select "Scan all local disks", schedule it then restart.
Please keep correspondance confined to the forum, that way everybody knows what's going on.
mayby its preventing the av scanner from running. some of the more advanced viri worms and trojans can. make so virus rescue disks and run them and see if that solves the problem. if it dosernt get clamwin av click here it is very slow but its totaly free and has a exelent av database. as it is not comenly use it may not be targeted.
Possible Mytob, but avast! isn't one of the ususal targets and even if it was the boot scan usually allows avast! to nail the relevant nasty before it's up and running. Clamwin is a nice backup, but I don't feel it's suitable as front line defence yet, having no Shield/On access style protection. The mail coverage also leaves a lot to be desired. OK if you use Outlook as a mail client and instal the addin, but its failure to cover Outlook express or any of the other POP3 options is a huge hole in coverage. I know it's on their to do list, but until it materialises.