I need to restore factory default set...

depending on the age and model, most acers come with a self-branded "recovery CD" creation program. I'm not sure why you need to do the restore, but assuming the computer will still boot, you need to find that program and have a couple cd's or dvd's handy and step through the prompts to create the cd's. Once you do, you need to restart the computer and boot it up with that CD you just created and step through the process. Make sure all your stuff is backed up first.