My Mac Mini outputs to my two new monitors - Dell U2311Hs.

The LED on the bezel displays blue when receiving a signal, or yellow otherwise. Both screens are displaying blue.

It also seems my Mini can see both of them...

However, one of them is black. It just displays black, but appears to be receiving a signal (when I turn the Mac off, it then displays No Signal).

To make things weirder, on startup, the boot up (white with Apple logo) appears on the right monitor (the one that now displays black).

Occasionally, it flickers up on the black screen for 1 second.

I have tried Detect Displays. It appears to do nothing.

I'm also running a dual monitor KVM. Video connections are DVI-D.

How can I fix this situation?

Thanks.

Update

This is the weirdest thing - I used the DVI-D cable that came with the KVM and it seems to have fixed it - I didn't both because it looks identical to any other DVI cable (in form an pin out).

So, I will accept an answer if someone can tell me what may be the difference in these cables?