Hi,
try deleting the files in SafeMode (F8-Boot), also clean your mailboxes and trash from the virus and compress the relevant folders in your email-Client (you might have to disable avast resident shield for cleaning procedures)
you want to read the virus infos an the avast home page about netsky variants, or
read herewhat WIN do you have ?
IF XP or ME, and the virus can't be deleted from RESTORE-folder:
disable System RESTORE first and reboot (or with XP: clean system, set a new retore point, and delete older restore points, via clean-up drive function in XP)