PTO won't engage

I was mowing and the PTO cut off. When I tried to engage it it seems to try but then it doesn't. Any ideas? I had a problem once before where I shut it off after mowing for a while and it would not restart. Would not turn over or anything. Called the dealer then and they said to let it sit for 30 minutes and then try it. That worked out and it started and mowed OK. Said That they've been having a problem with PTO switch but this seems to be different.

http://www.scag.com/OPManuals/STT/STTOPMANTOC.html

locate your serial number manual & see section 6 for PTO clutch adjustment.

Well don't I feel like a dummy. I pulled on the drive belt and it appeared ok. Good and snug. After continuing to try the pto it worked its way loose and I could tell it was broken. Mower only has 124 hours on it but I'm sure they will say belts aren't covered under warranty. This is the second turf tiger I have purchased new and the drive belt broke within the first year.

Anyone know what they costs now. Been a few years since I bought my last one.

Looks like about 40 bucks, that's a knock-off brand. Wouldn't be that bad if it were a V-belt, but that shows a cogged belt. I get all my V-belts at Napa, for all my mowers. They work just as good,and replacement costs are like 25% of name brand.