Trying to do this in Safe Mode.
SafeMode booting (repeatedly press F8 while booting):
http://support.microsoft.com/default.aspx?scid=kb;en-us;315222Can you schedule a chksdk there.
Instructions - Go to "Start", "My Computer", right-click on the "C:" drive, left-click "Properties", select the "Tools" tab, click "Check Now...", check "Automatically Fix File System Errors", then click "Start", "Yes" and Reboot. Repeat this for any other hard drive partitions in your system. Only the drive partition with Windows installed will require a reboot.
If you succeed... then you can schedule a boot time avast scanning...