The blades won't move on my black And decker 40 volt hedge trimmers. It sounds like the gears are not turning

SOURCE: Black and Decker 16 in Hedge Trimmer

I use a dremel with a sharpening stone, if u don't have one you can also use a power drill with a small sanding disk (1 inch) and course sand paper (30 or 40 grit). or you can use a bastard file. its too tight to use any kind of angle guide so just take your time and do it by eye. it shouldn't take much to get them sharp enough to do the job, over-sharpening is unnecessary and dangerous, and will make the blades dull faster. sharpen all the free blades, top and bottom, then start the trimmers to advance the blades to free up the sides you couldn't get. i use a light penetrating oil to clean the blades first, then lithium grease spray to lubricate.

SOURCE: Describe your Black & Decker Hedge Hog

You may have a piece of metal between the moving blade and the stationary one. Also the motor may have been at the top of the stroke when it stopped. You may be able to "force" the blade to move a little. This may free it enough to work.

SOURCE: Black & Decker Hedge Hog 24-Inch Hedge

You can definitely pick up a sheer pin for that model. I know ereplacementparts.com has them usually pretty discounted, or just check out a local store, but make sure they are in stock.

SOURCE: My Black and Decker hedge trimmer's blades won't

Your blades are stuck together.
Had the same problem: when I turn on the trimmer, the motor would hum but the blades won't move.
What I did:
1. Sprayed a ton of wd40 between the blades
2. Took a screwdriver and kinda wedged it between the blades to get them unstuck. Also removed some guck between the blades.
And it worked!

SOURCE: I have a Black and Decker 17" Hedge Trimmer

id check the electric motor first, was it whining when it was going? like maby the brushes in the motor are worn out. if so u can maby get replacements