Krell KAV 300i won't Power On?

I have a collection of audio much of which I never use and recently got this out of storage.

I once had trouble turning it on in the past, but noticed that the batteries in the remote were dead.  I replaced them, was able to power on the amp with the remote, and everything was fine, sounded great etc.

Now, I have just tried to use the amp (again with new batteries) but whether manually on the amp or with the remote, I can't get the red stand by light or the blue power light to illuminate.

I have checked the fuses in the rear which seem fine and also opened up the top cover where four internal fuses also seem fine.

Would greatly appreciate any advice or ideas whether specific to this Krell integrated amp or generally as to why an amplifier might not power on.

Thank you and best regards,