Was the unit sold as "not working"? If not, you may be best to send it back to the seller & demand a refund.
Assuming you did buy it knowing it was defective, the first thing I'd do is check whether it's the amp or the actual loudspeaker driver that's at fault.
That would involve taking the grille off and manually pressing on the loudspeaker cone to see if it moves at all (and if so, is there any sensation of scratching when it moves). If it doesn't move at all or there is noticeable scratching, then it'll need re-coned at least & possibly replaced outright.
You're best to do this with the speaker laid on its back so the cone is horizontal and press evenly by splaying out several fingers around the join between the main part of the cone and the central rounded dustcap.
If the cone does move freely, the next check is electrical continuity. With the speaker disconnected from the amp (you'll need to unscrew the driver from the cabinet and lift it out to get at the connections), using a multimeter set to DC resistance, check what value you get measuring between the driver's input terminals. It should be in the ballpark of 5 - 7 Ohms. Open circuit (ie infinite resistance) and it's definitely blown - again, a recone will be needed at least. If you don't have a multimeter, you can apply a 9V battery to the terminals instead - the cone should jump outwards a bit with the battery one way round and inwards with the battery connected the opposite way round.
Even if either of those 2 tests show the driver to be at fault, they don't tell you why it's damaged - the amp could still be the culprit.
Any further testing of that involves working on it with it powered up, which could potentially be dangerous.
If you're competent to work on it safely, again using the multimeter, check for any voltage on the wires from the amp, with the amp powered up but no signal present. There should be no voltage at either DC or AC. Note that most entry level (eg hardware store type) multimeters will only give accurate AC voltage readings at around mains electrical frequency - 50 or 60 Hz depending on where you are in the world. Any voltage at this stage and there is a fault in the amp - you'll need to find an electronics service technician to diagnose further.
Hope that gets you started.
(PS, I've pinged the mods to move this to the Junior Varsity section - the Forum Tech Support sub-forum is more about problems with the forum itself, rather than our gear).
