Problem connecting Dell U2715H monitor with Mac Pro 2008

What model Dell? and what video card. I would assume it is an updated card.

This

http://accessories.dell.com/sna/productdetail.aspx?c=US&l=en&s=dhs&cs=19&sku=210 -ADKB&ST=dell%20u2715h%20monitor&dgc=ST&…

says monitor is:

2560 x 1440 at 60Hz

and has:

However, you say yo are using a mini displayport to DVI adopter but the above does not say that the monitor has a DVI in.

Also, for resolutions greater than 1920X1200 you need a dual-link mini displayport to DVI adopter

I do not think the mini displayport to DVI adopter can be used in the direction you are using it. In addition the monitor being greater than 1920x1200 would probably not make it work in that direction

One of these will likely work:

http://www.amazon.com/SMAKN%C2%AE-Dvi-i-Dual-link-Female-Adapter/dp/B00M3WSF3W/r ef=sr_1_1?ie=UTF8&qid=1426192301&sr=8-1&keywords=dvi+i+hdmi+adapter

SMAKN® Dvi-i Dual-link 24+5 Male to Hdmi Female Adapter

I think yo need a dual-link adopter. there are also single-ling adopter

Yes. Dual-link card output>dual-link DVI to HDMI adopter>HDMI cable>HDMI monitor input.

A "standard" HDMI cable might not be sufficient. based on. I think yo need a high-speed cable.

Right now, there are only two HDMI bandwidth ratings: “Standard Speed” and “High Speed”. “Standard” is rated to handle 720p signals, though an over-engineered “Standard Speed” cable might handle 1080p as well. A “High Speed” cable is rated for 1080p and beyond, including the HDMI 2.0 spec which provides for 4k resolution at 60 frames per second, among other advances. It is the highest rating available today, though, an over-engineered “High Speed” cable may be able to handle the increased bandwidth of future ratings that don’t yet exist.

from:

http://www.audioholics.com/audio-video-cables/truth-about-expensive-hdmi-cables

Mini DisplayPort to DVI adapters are for connecting DVI displays to Mini DisplayPort computers. They will not work for connecting a Mini DisplayPort display to a DVI computer. A Mini DisplayPort computer switches to DVI when the adapter is detected, and the adapter sends the DVI signals to the correct pins on its DVI connector. A DVI computer cannot generate Mini DisplayPort signals, so the adapter won't work, even though it may have the correct connectors.

A DVI to HDMI adapter or cable will give you a picture since DVI and HDMI use the same digital video signals, but won't run your 27" display at full resolution. They take only single-link DVI (even though they may use a dual-link DVI plug) and connect it to a HDMI connector. Single-link DVI is limited to 1920 x 1200 maximum resolution.

You need a dual-link to Mini DisplayPort converter

<http://www.kanex.com/c247dl>

<http://www.amazon.com/ATLONA-AT-DP400-Dual-DisplayPort-Converter/dp/B003CWEXWO>

or replace your graphics card with one that has a Mini DisplayPort.

Time to leave the 2600XT behind.

The GTX 970/980 supports that monitor fully it seems.

http://forums.macrumors.com/showthread.php?p=20832436#post20832436