I held a key down while I was talking to someone on the phone. Now the key response is very slow and makes a clicking sound as the letter appears??

This is an educated guess on my part, but perhaps you invoked one of the "Accessibility Options" (http://www.microsoft.com/windowsxp/using/accessibility/default.mspx) in Windows. (I'm assuming we're talking about Windows here).

Go to Control Panel->Accessibility Options and see if any of the features are enabled. Then just turn them off and see if that helps.

Good luck,
WallyH