A common problem is the starting capacitor fails. If you turn on the unit on a hot day and don't hear the compressor kick on, that is likely the trouble.
You can replace the capacitor yourself if you are willing to get on the roof and pull the cover off the AC unit.
If the freon has leaked out, you are probably out of luck. The old Armstrong units had a valve for recharging but new units usually don't. Chances are that tracking down and repairing any leaks will not be cost effective, and buying a new AC unit will be the way to go.
When life gives you lemons, don't make lemonade. Go get the oranges that you really want.