1 of three monitors goes black for no reason

[DpR]

I have 3 2001fps. Two are connected through d-sub and a third with a digital cable. Just recently, about once or twice a day, the monitor connected with the digital cable turns black (same as when hibernating) for no reason. The other two monitor continue to work perfectly fine. I cannot get the 1 monitor to work again unless I reboot my comp.

The computer itself continues to think the monitor is working. I can move windowns over to that monitor (but cannot see htem obviously).

Any ideas? Thank you in advance for any input.