Think about anything out of the ordinary that may have happened the day (or day before) it quit.
- Was work done to your system?
- Did someone mess with your system?
- Smell anything odd?
- Especially loud?
- Did it quit mid-song or did it work yesterday and not today?
Assuming nothing special, here are some diagnostics you can perform. At the very least, they will help tell you what the problem isn't, First....
Eliminate power supply problems.
Use a meter to make sure you have power to your amps +12v terminal. A meter is preferred over a test light to confirm a full +12 volts.
Make sure the ground terminal is grounded. A meter with a continuity test option is best for this.
If either of these fail, trace the wires to find the fault. Large amps like yours normally have dedicated power cables. These cables usually have an additional in line fuse close to the battery. Check it.
If they pass, double check the amp fuse.
Pull the wire (usually blue) from the 'remote' terminal on the amp.
Then try jumping the +12v line to the remote terminal.
If it still doesn't power up, check for signal shorts.
Turn the gains down low.
Pull the input lines and try the +12v to remote jump again.
Next pull the speaker wires.
Your amp should now have only two wires and a jumper attached to it. Try the same jump.
If it still fails, the problem is in the amp itself and (I'm sorry to say) leaning toward the serious.
Hope this helped