If there are Symantec entries in your startup disable them, yes they could be causing a problem. Do you have any other Symantec programs on your computer?
If you do not have any other Symantec programs on your computer, go to Start-Run and type msconfig, press Enter, or OK then click on the Startup tab, uncheck any Symantec/Norton entries. Restart your computer then try repairing Avast again then restart once more to see if the changes take effect correctly.
I suspect Windows ME is part of the issue here, certain parts of Avast such as the Boot Time Scan do not work on Windows ME and I think the experts such as Technical and DavidR will need to continue here. if disabling the Norton remnants via the msconfig screen doesn't work.