Speaker problems..

I have a Resonance CD/FM/AM head unit (crappy, but it does the job) and 2 brand new sony xplode 6.5" as my "system". No rears, since I have a young child. I took them out. Anyways, here is my problem. One of my previous speakers that were in the front (kenwoods) blew, so I bought the xplods to replace them. I thought I could just pop out the olds and put on the new....wrong. For some reason, there is no sound coming from them. I even tried some different speakers and no sound output. I even got desperate and pulled the headunit and tried connecting the speakers directly to te speaker-level output on the rear of the headunit, thinking it may be the speaker wire...nothing. The headunit plays cD's and lights up, so it is getting power, but why no sound output. Any ideas? FYI, I drive a 86 4runner SR5 4x4...very nice!

I will check if any speaker wire is touching bare metal...but what happens if a wire did come in contact with bare metal? Would my head unit be fried?

I put in the headunit before installing the new speakers.

When you connected a speaker directly to the head unit without the installed speaker wires, were the "other" seaker wires still connected or were all the speaker wires out and "in your hand," so to speak?  If you have eliminated the possibility that any of your installed speaker wires are shorting to ground or to each other, then it sounds like the head unit amp is fried.  Sorry about that!  Time for a new deck.