You'll have to get to regedit through explorer, since obviously your keyboard won't work. If you HAVE to type something, you'll need to cut and paste the letters from other previously-created documents.

In regedit open this key: HKEY_LOCAL_MACHINE/Software/Microsoft/Windows/CurrentVersion/Run, and then delete a string value named DATCHECK.
Restart your computer and your keyboard should work.

Information on this program can be found here: http://www.dewasoft.com/Software/KeyPanic/KeyPanic.html
It's a VERY nasty little joke especially to play on inexperienced users