I'm thinking a switch. Or maybe a fuse.
If you get the multimeter, then you open the back of the cab, plug the thing in, and start following the power supply. Hold both probes in one hand only. Keep the other hand behind your back.
Repeat: KEEP ONE HAND BEHIND YOUR BACK!!
Find where the plug goes into the cab. follow the wires. when you see a place where the wires are exposed, look for a black one and a white one. You should get 120 V when you touch the probes (with one hand only. Keep the other hand behind your back).
Just keep following the power wires. Eventually you're either going to find a fuse, or a switch that power isn't flowing past. If you get all the way to the power supply, then test the leads coming out of it for voltage. Probably 12v and or 5v.
If you've got power going to your motherboard, and the game is still not functioning, then you've got a real problem I think.
For your purposes, any multimeter will be as good as any other. Home Depot sells some pretty decent ones for $20 or so, but even the super crappy $12 meter that Radio Shack sells will do the trick.
Did I mention you should keep one hand behind your back? And wear rubber sole shoes. Those two things are safety precautions that greatly reduce the chances of getting killed if you accidentally touch a hot wire.
I had a similar problem with my cab that had me stumped for a good half hour. Then I remembered that power switch on top of the cab. Doh!
Bob