Have you got the XP install disk?
Is your hard drive listed on the post screen?
Switching off by the plug wall socket is what we call a type of power out this can cause untold damage to your computer.
If you have the operating disk reboot pc and press some thing like F1 or F2 or Del wich ever you are prompted on your screen to enter BIOS/Setup.Set first boot device to CD/DVD rom put in operating diak then follow this link:
How to install and use the Recovery Console in Windows XP