So, I just got some new monitors, they don't have dvi on them, but have vga - hdmi - and display port, the issue I am having is I can go from the display port out on the cards "gtx 680 classifieds" to dvi without an issue, but it does not work the other way around, meaning I cant go from dvi to display port, I have the adapters to accomplish setting all of the monitors up and wanted to run them all display port, is there a special cable that allows you to output from dvi to display port? 
 
just to clarify, I can use the display port to dvi adapter I have to go from display port out on the video cards to dvi input on my old monitors without an issue, however I cannot reverse those same cables and go from dvi out on the cards to display port in on the monitors, no signal..
 
EDIT - PS I have 2 new gtx 980 classifeds waiting to install, is this going to be an issue on those cards as well? money isnt a problem so if there is something special I need to order I can get it.