2006 craftsman lt2000 won't crank

Hi there I have a question on my 2006 craftsman lt2000 riding mower with a Briggs and Stratton intex 20hp singal cylinder. Just recently changed the oil and oil filter and it started up just fine but when i went to cut some grass I turned on the blades and the moter sounded like it had no power so I shut off the blades and the moter picked up speed but when I turned on the blades again and I went forward and the moter quite all together and won't start back up I can even spin the moter over. Can anyone here help me please. Thanks