You need to be more descriptive if you want some real help, otherwise it is easy to understand why the mechanic didn't want to screw with your car.
Take an extra 10 seconds to think before you post, then another 10 seconds to proofread what you've posted. When it is easy to read and understand what you write, it is easier to feel good about trying to help you.
Since you said the stereo that was in the car previously probably just got ripped out:
A good start would be to make sure the illumination wire in the radio wiring harness (or any wires for that matter) aren't grounding or shorting out (behind the radio or in the gaping hole left behind).
If the amp turn-on lead (most installers use a single blue wire) was tapped at the fuse box make sure it isn't shorting/hacked off/dangling in there and while you're at it, remove and check all the fuses.
Check the terminals on the battery cable and try to look at the ground connection to the body if you can. Bad grounds make heat and can cause lots of electrical issues.
As a last resort, sometimes the blinker fluid gets low and we all know what kind of havoc that can play on an electrical system. :rofl: