Just an hour ago, i tried to play some guitar on my Spider IV 120, but when I started playing no glass was shattered!
I checked all my settings (amp & guitar) and my cables, i tried restarting & resetting the amp and even tried Test-mode. Nothing helped.
My amp itself wasn't the problem, since i heard it 'pop' during start-up and sometimes feintly heard some effect when changing channels.
Then i went online to search for a possible solution, sadly the only thing i found were people with the same problem as me.
I tried some more, and then i 'fixed it'. My girlfriend thought it was the cable, so i showed her when i unplugged the guitar there was no noise or anything comming from it.
I held it on my fretboard, which usually kills everything in a 30km radius, but this time i was happy to hear a small amount of noise.
Then i just (carefully) did that some more, and in 5sec my sound was restored!!
It's not something you should do every day, but it beats finding and getting to a service center & having to wait 6 months to get your amp back.
Just unplug your cable on your guitar's end, and gently stroke it against your fretboard until your usual sound returns.
I hope this can help some other people out!