This is a fairly common problem with the M200 series players (that’s why I switched to a clip). You can try the procedure in thread:
http://forums.sandisk.com/sansa/board/message?board.id=m200&thread.id=1501
It requires taking the M250 apart, but it’s out of warranty and doesn’t work, so what have you lost. I used it on two M250’s before mine locked up so tightly it wouldn’t reset.
