How to Restore Windows XP to Factory Settings WithoutHow to Restore free Windows

F8 is not for doing a factory restore, it's only startup options if Windows has issues.

Based on your system, you will have either a recovery partition you can enter with a key when the system is starting (F2 or something), or a set of CD/DVD disk to restore from. This will erase all of the data on the disk though, so don't do this unless you have a backup of your files or you get a new drive and restore the OS on that (which is what I recommend).