[NoiSeeVT]

you have to start eliminating things. If you disconnect everything from the amp except power, does it power up fine. If so you something outside the amp may be a problem

If it does power up fine add the speaker box. No input. This is a way to check the box

Now if that is ok add the input signal, if it then goes down, there is an issue with the input if not, reply and we try some other things

David