Please provide the model number when asking a question like this. Different models use different techniques.
Craftsman LT1200
Fix the drive belt.
check to be sure the blades have free movement. usually if you have this problem it is caused from something stopping the blades from rotating therefore it stops the engine
Your switch may be bad or came disconnected. Or your PTO could have came unplugged, or it went bad.
You probably blew a belt.
why does my rider cut off when i engage the blades
If you are saying that the mower shuts off when you engage the blades (or put the lever for the blades in the up position) then the most common problem is a bad seat safety switch. This is located under the seat. It has two wires going to it.
look for the engage switch that has a picture of blades
This has actually happened to me. There are some things you want to check.Make sure the blades are able to turn.Check your belts.Another problem might be with your PTO engage switch, these rarely burn out but the one on my tractor did.Check all things that engage the PTO, make sure all the lines and wires are connected and operational.My absolute best advice is to check with a dealer, but run over these things first so you don't go running to them with a simple problem.
There's a yellow switch in the upper right hand portion of the dash. It's the PTO drive. Engage your clutch, pull up on the switch and move it forward, and that should start the blades spinning. If it fails to engage, it could be a bad switch or a bad battery.
The term live power, or live power take-off, or just power take-off or PTO, is used to specify a feature of a piece of equipment like a tractor that has the ability to push or pull an aparatus, and also to separately drive the mechanical parts of the apparatus. In something like a brush cutter, the tractor pulls the cutting unit, and a separate drive shaft takes power from the tractor and transfers it to the cutter section to drive the cutter blades.
There's a safety switch under the seat. It will shut the tractor off if you get off the machine while the blades are engaged. It's not sensing your weight thinking you have fallen off the tractor.
Sometimes the belt will slip off the pulleys and sit almost where they are supposed to be and look OK from a distance. If the belts are OK then check linkage to see if something has come off .If it is an electric clutch on it then check switches loose wires and the clutch. Hope this helps.