Small Engines (Lawn Mowers, etc.): blades quit working, pullys, lawnmower

Question
My ridding lawnmower MTD use to work fine I have replace the blades but I have been noticing that when the grass gets just a little high the blades quit working the mower is still running but the blades are not. I have it on the highest setting, It didnt do this before, and has cut grass this high. Its really not that high it has cut grass higher in the pass.Can you help me? I was wondering if it was the belts but they look ok and with the engine off they are a little loose  

Answer
Well Laurie the belts are most likely the problem here. In time your belts will actually wear thin. This causes them to sit deeper in the pulleys and slip. You also want to make sure all the pullys move freely with the mower off. MTD is known for having bad bearings. Another thing I've come across is that the deck links wear and the deck moves forward taking tension off the belt. Start with the belt and go from there. GOOD LUCK