Qvis Viper nvr 4 no display on monitor

[keithy 0]

Hi have had this system for a couple of years with 2 x 3mp cameras ^ 1 5mp camera has been working perfectly until the other day when the display on monitor turned off. All i get now is no signal the nvr makes the right sounds but no display there is only an hdmi so no other connections to try.  If you go to the router its still there any ideas ? Thanks K