Metropol

I'm really confused and far too tired to properly sit down with it and talk things through like an adult.

Well, there's always another option for a bit of cathartic relief when dealing with iffy electrical gear.

I'm no expert when it comes to dealing with hi-fi gear but have you tried checking the output level of your source if it has one? Perhaps it's outputting too much for the amp to handle?

It sounds, smells, like a fuse may have semi-gone. This would explain the smell, the nonworking and working ness.

If your brave try opening the amp (after unplugging for a while) and see if you can see any damage or a fuse. Most amps do have an enternal fuse that can blow. If not, try setting the volume limit, I guess you've not changed it but its worth a try.

Out of intrest what amp is it?

Have you made sure that none of your speaker cables touch? That is the Poss and Neg of each speaker arnt touching (the metal beneath the sheath) My amp did this when one of my speakers cables were touching, may be worth a check.