Pretty much all monitors will accept either a DVI-D or DVI-I cable. And just about every video card I have ever seen that uses DVI is DVI-I by default, if only for compatibilities sake.
Do you have both the VGA and DVI cables connected to the monitor? If so, disconnect the VGA cable. It's useless and is probably what is causing the monitor to run in Analog.
If are only using the VGA cable, it will never run is Digital. You need to unplug it and exclusively use the DVI cable.
If you can run DVI, I highly suggest that you do. Aside from simplicities sake, you get better picture quality and response time from your monitor. The primary reason for improved picture quality is the DVI has significantly more available bandwidth than VGA; so it is able to send a more detailed picture. The other reason is that during the digital-analog-digital conversion process quite a bit a fidelity is lost resulting in a (comparatively) poor picture.
Hope this helps
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