If you are having trouble where the blades are not moving, this can be of great frustration. There is a few things you can look at to try get them moving again.
Check the nuts, bolts and screws are not too tight along the hedge trimmer blade.
Another area to have a look at and inspect is for debris on the blades. As the blades can often become clogged with sap or other substances this can then potentially stop the blades moving. This may also damage the blades if they can not move due to sap build up.
If there is sap build up also look out for twigs or foliage that may also cause the blades not to move. A way of preventing this build is to keep the blades lubricated. It is often recommended you lubricate the hedge trimmers before and after use.
WD40 or an equivalent lubricant is recommended to lubricate the hedge trimmers.
Check that no dings or marks are in the cutting blades. As this can damage the blades and cause them not to work at all, this would void any manufacturers warranty.