Try removing the db file from the nem folder and then start NIS again. It sounds like it got corrupted somehow.
It seems to be working now, blocks are updating.
Was to early with my happiness! I have 0 NEM in my wallet
Imported your private key ?
Using the right account ?
Headover to
http://forum.ournem.com. This problem has been solved many times there.
Oh, it's ok now. Of course it had to sync starting from 0. Wallet is up to date. Many thanks for your help mate!

Yes, just to be clear, when we sync a new chain, the balance will often say "0" as the chain is syncing, but then when it gets caught up to recent times, it will show the real balance.
Ok. Just one question: Is it necessary to activate "delegated harvesting"?
Not necessary, but it´s good for you, believe me. Do it, do it, DO IT ! (well, that was the short answer . .)
Then you will see by yourself, that this is one of the wonderfull features of NEM .
http://blog.nem.io/how-local-and-delegated-harvesting-works/In "Settings" just change "lokal" to a remote NIS, you can use any of
http://www.nodeexplorer.com/Then you can shut down your computer, and the XEMs will still come rolling in, if the remote NIS finds a block and the fees in it, which then is your´s . . No joking, it´s true, can´t believe it myself . .
And all that decentralized and with no risk, damn !