I agree with TWL that the burning plastic smell would seem to indicate some sort of fried part as opposed to just a popped fuse. Chances are that you probably will not be able to repair the amp yourself and since you can't seem to get the cover off sending it back makes the most sense. Remember: it's only an amplifier and it can be repaired. The downtime may pose an inconvenience, but I wouldn't lose any sleep over it.
Just another question -- do you also keep your preamp on all the time and are you sure the problem is isolated to the amp? Perhaps you have another amp you can substitute to check that everything else in the system is working properly...
Just another question -- do you also keep your preamp on all the time and are you sure the problem is isolated to the amp? Perhaps you have another amp you can substitute to check that everything else in the system is working properly...