DVI and D-sub input help

[higdongp4]

I just got a new computer with a blue-ray drive and an LCD monitor. My computer only has DVI connections and my monitor has both DVI and D-sub. I plugged the DVI cable into the two of them and it seemed to work fine until I began to watch a blue-ray movie. An error popped up and said I had to use the D-sub to watch the blue-ray. So I plugged the D-sub cable in and it works. But if I have both cables connected the only input that registers is the DVI, I have to unplug the DVI cable every time I want to watch a movie.

Question is: Can I fix the input problem some how and is there a way to have the DVI work for my blue-ray drive instead of using the D-sub?

More info:
I have the DVI plugged into the DVI and the D-sub into the D-sub. When the computer is started up before it gets to the login screen I can switch between the two inputs and it will respond, but ones I log in I can no longer switch between the two and only the DVI registers.

 

[Atomic Rooster]

Can you go into the monitor's menu and select which connection to use?

 

[ssc456]

that doesnt seem to make sense?

if youare watching a blu-ray then you need the DVI conenction should be the ova way around?

and infact it should be completely irrelivant what output you are using?
what are u using to play it?