Do you have an amplifier connected? If not, did you check the wiring from the cd player to the speakers to make sure none of them is pinched or shorting out anywhere? Have you pulled the speakers and checked each one individually to see if they are damaged or shorted out? If the speaker wiring is shorted out anywhere between the player and the speakers, it will cause the amp inside the cd player to go into protection (or burn up). If you have an amp, it could simply be that the amp is no longer powering up (either damaged, fuse blown for main power, or if your cd player has a fused turn on lead it could have blown). If no amp is installed, and you are sure the wiring is not shorted out, do you have each speaker on their own channel, or do you have more than one speaker wired to each channel off the cd player? If you wired more than one speaker to each channel, you could have damaged it due to low impedance that the player couldn't handle.
Check those things, and if you want to "test" the speakers without pulling them out, disconnect them from the radio harness (if you don't have an amp hooked up) and use a small battery (9volt works fine) and hold the negative speaker lead to the negative terminal of the battery, and then touch the positive speaker lead to the positive terminal of the battery, and listen for a small "pop" sound from the speaker. Don't HOLD the wiring to the battery, only touch it quickly to listen for the pop. If you hear a pop sound, without a GRINDING/CRUNCHING sound, then the speaker itself is probably ok.