My PC connect with my Arduino mega. But if i mount the ramps over it disconnect. I delete the stepperdrivers but nothing happens. What is wrong?

Maybe it's a dud. If you have a multimeter, check if 5v to ground is shorted. If not I'd replace the ramps board.

Check your endstops are not shorting 5v to gnd. This will stop a mega dead.

thx Dust. This is it.