Model #LST220 cordless, battery operated trimmer. I purchased last year but only use it 3 or 4 times a year to trim grass around family tombstones in a family cemetery. Yesterday I began to use it, then the trimmer line hit the stone and the trimmer suddenly stopped. I had plenty battery left since I had just inserted the battery but changed it out just in case. There is plenty of string left on the roll. The trimmer won't work. It does not make any sound at all. Any ideas what could be wrong