Viridian brings up a very good point. I have run across situations where fuses were not blown, but the device was not getting enough juice through the fuse to function properly. Kind of a "that shouldn't work, but it does" type of situation.
Sometimes just pulling the fuses and re-installing them can break up a resistive connection and restore proper operation. It is worth a try and cheap to boot. Just be careful and make sure that the amp is unplugged and the power supply discharged before sticking your hands inside of any electronic device.
You can typically discharge a power supply by unplugging the product from the wall and then turning it on. The circuitry will then try to energize, drawing power from the filter capacitors and discharge them. This could take time though, so let it sit for a bit while you do something else. The bigger the filter capacitors or "cans" inside the device, the longer it will take to discharge them.
This is especially true of power amps with no signal being applied. As such, you can simply leave the amp in the system, unplug the amp from the wall, turn the amp on at low level and continue to play music ( at reduced volume ) until you hear the volume dropping out quite noticeably. There may still be some residual voltage present in the amp at that point, but chances are, it is not hazardous. You can then remove all cables and proceed to inspect the internals as needed.
Hope this helps.... Sean
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