Dell u2711 keeps saying "entering power save mode" after replacing DVI cable with a Displayport cable

I own a Dell u2711 and I have recently started using Displayport cable rather than the DVI cable and the problem that I am facing is that the monitor is not starting after sleep mode, my system is having Sapphire 5670 card and I am quite sure that there is no issue with the cable, as I am not getting the boot commands I don’t think that there is anything wrong with the ATI drivers as well but then I don’t know why it just keeps on saying "entering power save mode" when the system is booting up and pausing at the dos commands before windows starts, I am not able to track out the cause of the issue but then I think that there is something wrong with either the Dell monitor or the sapphire graphic card that I am having, so I just wanted to know if there is any test that I can carry out to find out the cause of this issue, I really want to get it working anyhow and as soon as possible. Please help!!

In that case I will like to inform you that the monitor says its going into power saving mode when it is not able to get signal from the video card, I just wanted to know if you are getting "No signal" before it starts saying "Going into power saving mode", actually I have faced the above messages when I had started the system with the monitor connected for the first time, in my case I was also having a flatscreen TV connected to the card and I don’t k now why the card was seeing the flatscreen and was sending signal to the same even when it was turned off, I have found that if the Windows isn't starting in the DOS mode then the signal will go to both the monitors and it will chose the Default monitor and will cut the signal to the other when the control center gets loaded, in my case the connections were made using DVI and not Displayport but then I dont think that will matter if you are getting a no signal message as well, there are possibilities that your signal might be getting redirected to some other port as per the preference that you might have set in the control center, so just check out these things and then let me know if you are having the same case.

My system specification is as followed:

• Intel i7 960 based PC with 6GB on memory
• Gigabyte GA-X58A-UD5 Rev 1.0 motherboard. (LGA1366)
• SSD boot drive, WD Green 2TB standard plater data drive
• Sapphire HD5870 Vapor-X 1GB video card
• Windows 7 Ultimate 64 bit

I am also having similar issues with non-Dell PC and an ATI card, in my case some time when I move the mouse then the monitor will come out of Power Save mode but the it used to take long time to come out of Power Save mode, I have been using the power save features in Windows for putting the system to sleep but the when I used to power down the monitor then power it up again then it was helping me out in bringing the monitor out of Power Save mode, I had tried out changing the source but then it was just not making any difference in my case, sometimes when I used to power down the monitor then power it up again then I used to get a "Displayport Link Failure" message on screen but then it was due to open windows at the time, I had found that this issue used to occur mostly when the monitor has been set to 1024x768 resolution but then when I used to wait for the monitor to blank out and then power down the monitor and turn it back on immediately then the open windows was not getting resized and it used to come up with the correct resolution ie 2560x1600 when the monitor used to come back from the power down/up, I think that this issue is with the Displayport cable, I have searched about the same in a number of forum and have other having similar case as well.