When you say you've checked that cables, are you saying that you have checked with a multimeter and they're showing 12v+ across the live and earth in the boot (or wherever the amp is mounted?
You've checked that the remote wire is also outputting a voltage?
Does the amplifier iteself have any on-board fuses and if so have these been verified as ok?
IF the answer to all of the above quesions is YES! then I'm afraid your amp is toast.