Your title and comments suggest different problems.....
If there is no tention on the blade engage lever, the most obvious thing to check would be to ensure that the cable is not broken.
The engine stopping when the blades are engaged is a symptom of a failed seat safty switch. This is located under the seat, and it's purpose is to shut the engine down if the operator falls off.
phil_saunders@bigfoot.com
Phil Saunders
September 2008