|Your Windows installation has probably been corrupted by a power surge during the storm, or if the PC suddenly lost power and Windows couldn't shut down in the proper manner.|
Re-install Windows from the recovery discs or the Windows XP CD.
If no CD, with Dell computers you can sometimes start Recovery by pressing
Ctrl + F11 keys together as soon you see the Dell splash-screen when you switch on. That's assuming the hidden partition containing the recovery data still exists and nobody has removed it or replaced the original drive.
Some older Dells weren't supplied with a Recovery partition so the Ctrl+F11 method won't work on them.
Depends what model your Dell is and when it was built.