Has Something Tripped?
The location of possible tripped devices is not limited to your main panel. Besides reset buttons on garbage disposals, water heaters, and on some in-wall heaters, there can be circuit breakers or fuses in a subpanel far from the main panel. Look in basements, closets, utility rooms and behind pictures, mirrors, and doors. If you have a box of generator switches, one of those might have been knocked off accidentally.
Rather than a fuse or breaker, a ground-fault interrupter (GFI) receptacle could have tripped. My hints for looking for these devices relate to the rooms they are commonly in; see GFIs. Also, at a dead outlet there is a Test you can make to tell you how likely it is that it is dead from a GFI that is tripped somewhere else.
Suppose you are at your main panel or subpanel or a fusebox. Can you easily tell (from looking) that nothing is tripped or blown? The answer is NO. If something is obviously tripped or blown, fine (although it could represent an ancient problem someone else gave up on long ago -- not your present problem). No, very often something can be tripped or blown and be hard to detect. The surest way to find out is to Test for hotness at the circuit wire where it leaves the breaker or fuse terminal; that terminal screw itself is usually just as good a place to test.
If you are avoiding this test from a concern about safety or from laziness, a second best procedure is to very firmly push the handle of every breaker in turn firmly to full "off", so that it perhaps even clicks in place, and then firmly click it to "on" -- but don't be holding it on, especially if it is buzzing or humming. This is the right procedure for resetting any breaker. "Flip the breaker back and forth" is simple-minded and misleading.
A third best attempt is simply to weakly press each breaker handle a little more toward on (or later toward off, but without turning it off) and notice if one breaker seemed to have more give or play to it than the others; then do the off-then-on procedure just on it, remembering which one it is.
All right. If you have not succeeded in resetting a breaker or still aren't sure if any have tripped, what should you do next? Get help from the Diagnostic tree.
"We lost power on a circuit and we thought we were resetting it but it actually wasn't turned off all the way... your site said don't be shy and sure enough, it wasn't fully tripping and now the tankless hot water heater is back on and working as well as the lights..." -Tim
"I fought my GFI breaker and won thanks to you! I'd tried everything to reset it and it seemed to reset but then there was still no power at the outlet. I tested it to see if something was wrong with the breaker and it would trip so I knew it wasn't that. Then I saw on your site that you may think you've turned it off but unless you pushed pretty hard and hear a click you probably didn't really turn it off before you turned it back on. That was it! I've just had the worst week ever so to be able to figure this out on my own was a small triumph but it was big to me. I'm a single female and I hate to have to pay big bucks for a service call over something stupid like that. But I'll happily donate a few bucks to your site! Thanks, again." -Marsha