Stereo problems

[jlc1210]

I have a 2001 Dodge Neon SE that came with the standard AM/FM cassette stereo. One of my daughters bought me a cheap AM/FM CD stereo for xmas from Walmart and I made the mistake of letting my son-in-law attempt to put it in. First, he wasn't aware that you had to purchase and install a plug kit onto the back of the new stereo...so he tried to wire it in direct. Of course, he couldn't. So, he put my old one back in. When he did, it didn't work. Neither did my dome light (but the cigarette lighter does work so don't suggest that fuse), and the digital mileage gauge blinks back and forth between the numbers and fuse THREE times before stopping when the car is first cranked. I know I should have a professional look at it. Do I take it to a stereo shop? or the mechanic? He's claiming there is a short in the system but it was working fine before he got ahold of it.
THX !!