Stock 1998 CD Player replacement

[72Blazerod]

I have the AM/FM/Cassette stereo with the separate CD player in my 1998 GMC Suburban. The original CD player seems to be pretty worn out, it skips a bunch and doesn't like to play any CDs when its cold out. So I found a used stock 1998 stereo with the entire AM/FM/Cassette and the separate CD player and bought the works. I thought I'd just install the new CD player because the rest of my existing unit seems fine. When I finished plugging in the new CD player it will not play CDs. Am I missing something? Is there a code or something that won't allow a CD player to play with a different head unit? Should I switch head units so the 'new' CD player is hooked to the original AM/FM/Cassette player that it came from the factory with? Or did I just buy a dud replacement? Let me know what you think.

Cheers