Dell U2715H stuck in PowerSave mode on MacBook (EDID problem?)

Hi,

I purchased the U2715H monitor instead of the Apple Cinema Display as it was strongly recommended by several Mac review site. However, when comes the time to plug it in my MacBook (late-2008 Aluminium) through the MiniDisplay Port (not ThunderBolt), the monitor instantly goes on Power Save Mode. The only way I can use it is through a HDMI adapter and then, the resolution maxes out at 2048 x 1152.

From what I understood on different sites, it is possibly a problem with the EDID of the Dell Monitor on the Mac OS (I'm using Yosemite right now). It is possible to override the EDID through a Ruby Patch but in order to do that, I would need to be able to plug the U2715H through the MiniDP, put the Mac in Clamshell mode (close the MacBook so only the secondary screen is used) and then start the Ruby Patch to create the appropriate DisplayVendor ID. However, because of the aforementioned problem, it is impossible to do so (screen automatically goes in power Save mode and is not detected by MacBook even if the MacBook screen flashes when I plug the MiniDisplayPort cable in). See http://embdev.net/topic/284710

Is it possible to create the DisplayVendor ID override for the U2715h (it would be named DisplayVendorID-10ac)?

Or is it that the graphic card in the MacBook (NVIDIA GeForce 9400M 256 MB) is unable to send Dual-Display through a MiniDisplayPort cable (it can through Dual-DVI however)?

Any help would be greatly appreciated.

Thanks,

Dom