to test a wall outlet for 120 A/C you put both red and black leads into both sides of the socket, not on the 3rd ground pin because you are measuring both "legs". set the multimeter at A/C 200
here is a quote from a member here who i've forgotton his name(please forgive me)
but i havent forgotten his words:
"AC is not DC, and as such where you put the leads is a little different. With DC and electronics, there's usually a common ground. With AC, there is no common "ground" so to speak - there's the two AC wires, so you need to test between those two.
Secondly- since AC is a lot more lethal than the 5 and 12v dc we usually play with, please be careful dealing with the fuses, I think the AC fuses are not protected and can kill if its plugged in and you touch the wrong thing.
Basically, look at the power brick and follow the cord as it comes in. Unplug it and dust off the wires with a cheapo paintbrush or shop vac if need be. It'll be very easy to follow once you see how they go. The cord is going to come in, prob go through 1-2 fuses to fuse the actual AC power, then split to feed the two transformers - one is an ISO that feeds the monitor, other other makes the lower voltages that feed the board. Those lower voltages in this case are still AC so you need the AC mode to read them.
Here's an easy test - if you put your meter on AC 200v, and read across each fuse (one lead on each end off the fuse) - a blown/bad/dirty fuse will show full voltage. A good fuse will show no voltage across it."