What could be the problem with our inground pool?

Here's what has happend: 2 days ago we noticed the filter, etc was not running. We flipped the switch and nothing happened. We reset the GFI and voila...it started to work! 2 hours later everything was off again. We tried to reset the GFI and nothing happened. 4 hours later everything went back on again without us touching anything! Thoughts? Is this an electrical problem? Motor? Of course it's a Sunday and I'm getting nowhere fast....and in the mean time its 115 degrees out and I'm pretty sure if we watch closely enough we can SEE the yellow algae growing!