Keyboard and mouse inoperative (by 2 users)

The wife's aspire 1640 boots to the "click your user name" page but the mousepad only works slowly and we can't enter our passwords to get into our accounts. I've set the bios back to default settings and rebooted. the system will then allow me to type in the first 4 letters of our passwords but no more and will only allow this to happen once. I'm sure it has virus problems but can't get in to resolve those.