Does your debug log contain any useful clues, such as an error like "coinstake attempt failed"? My log is full of them:

04/19/17 22:34:39 coinstake attempt failed
04/19/17 22:34:40 coinstake attempt failed
04/19/17 22:34:41 coinstake attempt failed
04/19/17 22:34:41 connection timeout
04/19/17 22:34:42 trying connection 84.168.117.1:17177 lastseen=9153.6hrs
04/19/17 22:34:42 coinstake attempt failed
04/19/17 22:34:43 coinstake attempt failed
04/19/17 22:34:44 coinstake attempt failed
04/19/17 22:34:45 coinstake attempt failed
04/19/17 22:34:46 coinstake attempt failed
04/19/17 22:34:47 connection timeout
04/19/17 22:34:47 coinstake attempt failed

I can start the client, but since I have a zero balance, and PoW mining no longer works, I can't do anything to extend the chain...