How can I fix my 1890`s mantle clock?

My clock worked fine up to xmas. It has an eight day movement but recently after winding only went for 6 days then to 4 days then to 2 and now won`t go at all. At the moment it is fully wound but won`t go for more than a couple of minutes. It is an 1890`s slate mantle clock with, I think, a german movement.

Julie Harris
January 2007