Keyboard:  Standard 101/102-Key or Microsoft Natural PS/2 Keyboard, Name Enhanced (101- or 102-key)

Used on Dimension 8250

Make or buy a tweezer with the ends bent in about 1/32 or 1/16 inch.  They can be purchased as chip pullers.

Manuever around the edge of the key until the tips slide under the edge of two sides of the key.  Pull up gently (about 1 pound of pull or thereabouts will spring the key cap off.

Then you can clean what you see on the keyboard and around the underside of the key.