Cant get sound from speakers... HELP!!!

I changed from one aftermarket head unit to another and now i cant get any sound from any of my speakers. The head unit is acting completely normal and my subwoofers work as well. But nothing plays through the speakers. Everything is connected properly in the wiring harness (believe me i checked... a lot) and nothing else appears out of place. The head unit i had before this one worked perfectly fine. I'm totally stumped. Please help.

"The head unit i had before this one worked perfectly fine. I'm totally stumped."
I think you have answered your own question.:)