This will be one of four things:
1. Dirty condenser (preventable)
2. Burned out compressor start relay (very fixable)
3. Bad or lazy condenser fan motor (very fixable)
4. Bad compressor or sealed system ("freon") leak (terminal event: go shopping)
As indicated, the first three causes are very fixable, even preventable. But the fourth one is a 4th Down Time to Punt
event. That's because EPA's DuPont regulations
have made doing sealed system work so expensive that it's not cost-effective to do it on most refrigerators... unless you paid so much for the box that you're married to it (a la Sub-Zero). So, lots of easily-repairable refrigerators choking up the landfills today.
Be that as it may, let's talk about the first three things that we can do something about...