wierd ground makes car not start

Read the grounding stickies at the top of this forum.  If the fried amp is shorting out your electrical system - or part of it, like the fuel pump due to an improper installation - then it could cause the car not to start.  I suggest you need to get help from a professional since this is apparently a problem beyond your skill level.

That's what has me puzzled - if the amp was causing some sort of issue that is preventing his car from starting it should blow a fuse.  The car shouldn't not start with the ground connected and then immediately start right up once the ground is removed.

When you say the car won't start what do you mean?  Will the starter crank but the motor won't turn over?  Or does it not even crank?  Also, what happens if the car is running when you ground the amp?

Ok, ran a couple of tests at lunch. The amp works with the car not started. The motor will not turn over, it just cranks and cranks and cranks until I drain the battery. I have not yet been able to test wether grounding the amp with the car running will kill the motor.

The car shouldn't not start with the ground connected and then immediately start right up once the ground is removed.   => This is exactly what is happening.

Then, like I said, you need to get someone local to help you.  An automotive electrical shop might be in order.  For whatever reason your amp is shorting out your fuel pump - maybe.