U2715H entering powersave mode

Hi,

I've got an issue with a relatively new U2715H.  It was working fine, though I now can't get a signal from my desktop (Windows 8.1, Nvidia 670GTX, latest drivers). 

I've tested with my laptop (mini DP) and monitor (DP) and it works ok. 

However, on my desktop, I get the "Entering Powersave Mode" when I try to connect to it.  I've tried HDMI (both ports) and DVI to DP.  I've done a factory reset, though can't get any signal from my desktop on it.

Any suggestions?

Thanks,

Mt