1/2 dead recepticle

If all of your outlets on that circuit work properly but that one, it is probably the last one in the circuit. So the power is coming in to the top sets of screws on the outlet. Check (with power off) to see if it has only one set of wires going to it. If it does then the one of the jumpers between the screws on the side of the outlet are probably broke. I would check this first. You can visually inspect but can't always see the break. So if upon visual you don't see a problem then I would check for continuity between the screws. You should be able to check with a multi-meter whether you have continuity between the silver top screw and the silver bottom screw and the same with the brass screws. Hope this helps. If you don't have a multi-meter I would just buy a new outlet and replace it. It sure sounds like a broke jumper. Good luck and be safe. Make sure power is off.

Two reasons for a receptacle to only work on top half.
Some broke the tab off or the receptacle is defective.
If the tab is off then it could be a switched receptacle. Do you have a switch near by that you can't figure out what it controls.
The tab could also be off because it is fed from a different breaker. It sounds like yo may have some split fed receptacles and one of the breakers is tripped.

I belive they are split (on the main breaker panel they are named "kitchen splits" . But there are not switches controlling the plugs.