DVI-I output only giving Analog video signal : Optiplex 745 USFF?????

[mjavid]

I have a Dell Optiplex 745 USFF system (which I'm using to post his message!). It has a DVI-I output, which does not seem to be sending out digital output (no signal when I use a DVI cable that was working fine previously). However, strangely, when I use a DVI to VGA converter plug, it gives analog output! Is this even possible? Is the board or connector defective?

I know that my DVI cable and monitor are OK, as the DVI output of my ASROCK Z-68 works fine.

The above problem occurred when I disconnected my system to transport it to my office. When I reconnected it, no DVI output.

Please help!