Hello Headcrabs there are a couple of ways to do a restore.
Fisrt try and go back at least 5 days before the problem started and do a computer restore. If That does not work and you want to do a full factory restore then you will need to have either the factory recovery disk's or the full purchase program disk's and you put it in to the drive and then turn off your computer, then reboot and when the instructions come up on your screen it will guide you through the process, a full factory restore takes a while to do.
However I do agree with Niemiro 100% and I recommend you follow his advice first before doing the restore.
I would also do a full AV scan plus download malwarbytes and run a full scan so you can mark those off the list, this way it will tell us if you have been infected.