2001 Tahoe it's spinning but won't start? Help?

No one can tell you what's wrong with your car without checking it. Most likely it is not getting fuel or does not have spark. Listen for the fuel pump to run as you turn the key on without cranking the engine, if you hear it run you'll need to see if it has a fuel pressure test port on the fuel rail to verify that is OK. You can check for spark by pulling a plug wire off one of the spark plugs and inserting a spark tester to see if spark is present as you crank the engine. If spark and fuel are present then the engine could be flooded (wet spark plugs) that won't fire or worst case scenario would be the engine has gotten out of time, if that was the case the engine would sound different than usual when turning over - like it's spinning too easy. Good luck.