Why won't it start

What is your question?

Hoked battery up backwards.then replaced main fuse. When you put key in run position and the check engine light comes on, it wil start. Turn off and turn key back to run and light doent come on and no start. The car will only start once every 6-8hrs. When it starts, you can drive anywhere as long as you don't shut it off. What could cause this?