Did you build this PC or is it a pre-made?
It could be a number of things :RAM, Video Card, CPU, Motherboard, HDD but I doubt the power outage did anything to it. If you are somewhat comfortable handling components read on if not put her in a box and ssend her to her maker.
Below is the Computer trouble shooting guide for dummies(not saying your a dummy but just inase

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1. With the Power Supply UNplugged and your seflf grounded procede to remove the case.
2. Remove any unneeded hardware such as modem, NIC, CDrom, DVD rom, Floppy(not the harddrive yet) and try the computer to see if it works good if not step 3
3. Take out 1 stick of ram and try the computer if it still dosent work try the stick you took out and take out the stick thats in...or you could test the ram in a different computer or try ram in your computer from a different computer. Ram not the problem step 4
4. Remove video card and use integrated video(if you have it) or find an old working video card to test. If you PC is still acting up it will require a trouble shoot of the hard drive,cpu and motherboard wich I doubt you are very equiped to do and scence you only have a restore disk it means you probably got it from a company so send it off and tell them you want a real WinXP disk and not a restore disk also tell them not to charge you for it... Hope I helped some and Qs ask
