how can i fix my grandmother clock?

It may just need cleaning. Cased clocks gather dust and airborne particles quickly.
You could try one of the "dry" duster cans used for computer keyboards (I have "Endust") just keep upright (the can, not you!) and do NOT shake - it emits a hi-pressure neutral gas that will clear accumulated crud.
If that doesn't help get a clockmaker to give you a quote.

Zipper
December 2010