I had the same issue with the amp not coming out of standby anymore, just weeks before it got 2 years old.
I had one of the original Bugera tubes go out of specs (at least Infinium showed this to me with an LED being constantly lit), therefore I decided to swap out every single pre and power tube for JJs as I considered them to be of higher quality and sound better.
Whatever this might mean...was just curious...
So I took the amp back to the rehearsal space and fired it up, and it really sounded a bit warmer, fuller and with just an ounce more clarity in the highs.
After 2h of playing we took a break for the smoke addict band members, so I just turned the volume off on the bass guitar and kept the amp fired up.
When I came back, the fault/standby LED was red instead of orange and I tried to put it into standby and back to operation with no effect.
Same with full power down, cool down and fire up again - it wouldn't come out of standby anymore.
So we ended rehearsal there and I took it home to take a look.
I found one of the brand new JJ 6550s having a little hole in the glass bulb, and some white dust inside.
Ok, tube death...sh.t happens.
Had a new tube shipped over to me, even matched to my other 5 ones by the store, plugged it in and - nothing.
Still wouldn't come out of standby.
So I had it sent in for repair under warranty conditions, got it back 2 weeks later and all fine again since then.
And yes, it was my unit that I got back, it still had the JJs in and the same scratches at the housing that I added to it by accidentally "road wearing" it.
Still I really love this amp so much, it sounds amazing and is able to easily release an earthquake with my sweet little custom built 2x18" cab.

I especially like the preamp and its sound controls, so I can't wait to try the new Veyron T, hoping it to be a similarly sounding but more portable version of it.