When I set my thermostat on cool, my outside ac unit won't kick on if I set the thermostat past 73 degrees. It cools the house to 73, kicks off, then kicks back on when the inside temperature in the house goes over 73... so its kind of working but only at 73 or under... it worked normally before where I could set it at 77 degrees and it would go on & off.

Sounds like a defective thermostat to me most likely.

Get a good thermometer, and see what the actuall temp in the house is, right next to the actuall thermostat. Your stat may be out of calibration, in which case, a new stat is most likely the answer, as smoothy suggested. If the actuall temp of the home is below 77, then it won't kick on till it gets hotter than 77 in the home. And if the stat is out of calibration, it may be off by several degrees.