My AC unit has been running for several hours, but the house is no cooler than when it started. What could be my problem?

Check your breakers in the breaker panel it will be a two pole breaker, also check your fuses at the outdoor unit ( they will be in a box on the wall ajacent to the A/C unit outside) May be the outdoor unit is not running.
You might also take a water hose and wash the condenser (outside unit) if it is low on refrigerant you will probably have to call some one, let me know if this does not work and i will give you more things to check. Mike

My AC unit has been running for several hours, but the house is no cooler than when it started. What could be my problem?

Mine did that, and I had grass clippings inside the grates of my a/c unit. The line was frozen going into the house. Needless to say, I took my garden hose and flushed the clippings out of the unit. That's what my particular problem was. I'd follow the 1st reply to your question.

In addition to the above mention, check and be sure your air filter is clean. You can open inside unit up and look and see if the coils are iced up.Is both the inside and outsid fans running?