After hitting a rock, motor runs but blade does not turn.

SOURCE: I have Black and decker electric lawn mower does not start

one of the problems i found with electric detectors was that they do not tell you if there is a break in the neutral cable so you could have a break there,another problem is that the levers can break inside the cover giving the impression that it should work but is not making contact with the switch ,hope this helps

SOURCE: electric mower won't cut well

change a new blade. when was the last time the blade gotten changed?

SOURCE: Black and Decker 18 inch electric lawn mower turned off

Try the link at the bottom of this page : "Find Manuals".

SOURCE: I have an old Black and Decker 18 electric mower

Here is the black and decker website:

http://www.blackanddecker.com/ProductGuide/CategoryOverview.aspx?cPath=1498.1670

Most the old models where 6 amps. 1/2 hp

You can get another one from ebay or craigslist

SOURCE: WIRING DIAGRAM? FOR BLACK AND DECKER ELECTRIC LAWN MOWER MM 850

looking down at the terminals, rotate push-button to the right. the wiring sequence is R, W at the top, then Black (in, from power source) , Black (out, to motor).