Nis.exe 100% disk usage Windows 8.1

Whenever I boot I get 100% disk usage which lasts for ages and then keeps happening frequently, making my PC impossible to use.  The only activity seems to be nis.exe which is both reading and writing to disk at a very high rate.

I have tried the usual disk usage fixes such as disabling Superfetch and Prefetch, but it's made no difference.

Any suggestions?  I'm desperate.

Thanks.