I was mowing today when my Toro wheel horse rider model 70040 (electric start) began to slow down. I was driving along in 4th gear, and I noticed it was going pretty slow, it felt more like 2nd. I stopped, backed up, thinking there may have been something under me slowing me down, and it reversed fine. Then, I started to move forward again, in a low gear, and it seemed OK, but I shifted up and it still moved slow.

I shifted into neutral and let it idle until it died, and now I can't get it to start, although it's in neutral, blade is disengaged, etc. I bent down and looked at the belts and they look OK... but I tried to push it forward or backward and it won't budge. The wheels just won't turn, and it won't start. With these two symptoms, what could be the problem?

Forgot to mention that nothing happens when I turn the key. I hear one click. But engine doesn't turn. When I look at the belts from the back, one of them looks very loose. Is this a belt issue or an electrical issue?