If you had two speakers I might guess that you had them wired out of phase. (the + and - plugged in backwards on one of them)

As far as being blown, you can check most speakers by just pushing in on them. If it feels scratchy or has resistance then there's a good possibility it's been blown. And contrary to popular belief, most speakers are blown from being underpowered and driven with too much distortion as opposed to turning them up too loud with a powerful amp. For instance, you can blow a speaker with a 20 watt amp turned way up because all it's doing is putting out distortion which quickly heats up the coils. A more powerful amp can rarely blow a speaker but rather than burning the coils it's usually literally blowing the cone out of the speaker casing.

Other than that, I'm at a loss. Most of my experience comes from stereo systems so I'm not too familiar with amp problems.