|And if there are files etc. that you would like to save - regardless of what you may have to do to re-enable the system…; particularly if going for a Factory reset/restore (using the recovery partition) or re-installing the OS via an XP disk - then be aware…|
If you do any kind of reset/restore routine - it will erase all files on the computer in the process - including your personal files. So very wise to save them first.
Download an Ubuntu ISO save it to a hard drive, burn it to a DVD. Boot up with that DVD, and you can access the hard drive on your faulty computer, copy/save those personal/special files to an external location; typically DVD. Check the copies are accessible on at at least one other working system; then put safely to one side. You can later (if needs-be) restore them to your rebuilt/repaired etc. computer.
ubuntu.com - the ISO is a freebie download.
Note that if you do download and burn etc. an XP ISO (from the site Riider suggests) you likely will need to get the OEM version - not the retail. Most pre-installed systems come with an OEM installation - not a retail version. Thus the key you have for your installation is likely an OEM and will only work with an OEM version.