CLASSIC...

Look in the technical section, setting up RC valves.(http://www.nsr-world.com/tuning/250-tuning/engine/) Disconnect the cables and run it through the test cycle, to see if its the RC valve stuck, or the servo or PGM cooked.

If its the valves themselves, pull them out, clean them thoroughly and put them back in, reset...

If its upstream of the valves, get hold of another servo, plug it in and test. If it still doesn't work, get another PGM, plug the newest servo in and test.

Word of note: PGM's don't cook servo's generally. Servo's cook PGM's.
Usually because the valves are coked up and siezed or adjusted too tight...
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The Chopster