If you look above where the mains lead plugs in, that’s an inline mains fuse holder. Just use small screwdriver to lever it open. It’ll hold a 5x20mm fuse – which would have detonated if either of the loose wires contacted live. That seems likely if it tripped your mains.
These fuses can be obtained from maplin or the like. Often there will be a spare hidden inside the fuse holder (it holds one fuse which connects across the terminals and a second behind that). Probably be 2A or 3.15A for that amp, might be T2A or T3.15A (this is a time delay for the fuse). This will be stamped on one end of the fuse that you remove, in case you have to remove it. If you can’t get to maplin or the like, send me the value and your address and I’ll post you one. Email on profile.