Black & Decker 18" hedge trimmer, TR1800, has worked fine until yesterday, when I plugged in the trimmer, heard the motor running, but the blades were stationary. I had not run the trimmer into a thick branch or any obstruction during previous uses of the trimmer.

Manuel Zax, June 2005

Mine (black and Decker) was the same, you have broken the clutch mechanism!
Take the bottom off the unit (4 screws) and take the blade unit off, here you will see a gear which drives the blades back and forwards, with a offset pin, I drilled thro the two pieces, slightly c/sink both sides and put a small shear pin thro, then hammer the two sides together and the file excess away, replace and all should be well, if it shears too quickly increase the pin size, but not too big, it needs to shear if you hit something hard.

davey, June 2005