HDMI monitor going black intermittently
 

Installed a new targus dock with my dell laptop and LG HDMI monitor. It worked straight away and was happy with the result.

After a few hours the screen just went black, no matter what i tried it wouldnt not activate, if i unplugged the monitor and inserted direct to the laptop every thing works fine including other devices in the dock.

i checked all the drivers and reinstalled the display link driver and changed the monitor to extended monitor. Rebooted everything and it all worked fine. Then it just went black again like it goes into sleep mode, i unplugged and plugged into laptop and monitor came alive i then replugged into docking station and it worked again.

Any ideas would be great to resolve this