Could be the radio. I replaced my radio and speakers myself.
I used Kenwood Excelon KDC-X799 and Polk Audio db651s 2-way Coaxial speakers.. I removed the dash tweeters.
It is easier to just replace the radio.. or at least take the radio out and check the connections.
The Door Speakers don't use normal Leads, but instead a connector. so unless they're unplugged.. it sounds more like a problem in the radio
Just fyi, I have the stock radio I pulled out of my 07 to install a touch screen. I think the CD drive motor is messed up, but you may be able to cann parts off it to get a solid working one. OP or anyone else is free to have it, just ask that you pay shipping.
Three systems are available on the '07, the base single DIN one, the mid-range double DIN one, and the Navigation one. But you didn't specify what you have. If the tweeters are working, first check the balance/fade/other adjustments in the radio to see if one is set wrong or anything changes when you change the adjustments. If you don't find a solution doing that, I would just take it to a reputable audio shop and have them test it. They will have meters to see if the speakers are getting a signal, etc., and whether all the grounds and speakers are good. A reputable guy can do it in half an hour and won't charge a fortune, so ask first.