I'm assuming you're talking about an aftermarket head unit?
I've installed many Pioneer's, but I think that they're all similar.
- Remove the detachable face (if it has one)
- Remove the plastic bezel (it comes out really easy if you pull up/down from the middle to release the tabs)
- Insert the removal keys (likely an L shaped piece of stamped sheet metal, and there will be little pockets between the sides of the deck and the metal housing)
- Then just pull the deck out
It might be easier for you to check the fuses in the main panel first.