Help with blown amp

I have a Plinius SA-102 amp which I have had for a few months. It sounds great and I have never had a problem with it. This evening, I was in another room, not listening to music. The amp was on as always, but no music was being played. All of a sudden I heard a loud hissing sound which lasted for about 3 or 4 seconds and then a click. The amp has an automatic mute switch which kicks in when there is a problem. When I checked out what was going on, the mute switch was on and I could smell burning plastic. The mute switch will not go off, and the amp will not work. I immediately unplugged the unit and tried to remove the top lid (per the instructions) to see if one of the fuses has blown. Unfortunately, I can't unscrew some of the allen nuts as they are too torqued.

Can someone please help me get a good night's sleep and tell me that it's only a fuse? Could it be worse? Any ideas on how to get overtorqued screws out?

Any help would be greatly appreciated.