Recently, I brought a Dell U2713HM display, with resolution of 2560 * 1440. And my current computer have a HD6800 ATI card.
Then when I connect display with DVI cable, it turns out that the highest resolution I can set is 1920 * 1200 in the windows settings. That’s sucks.
So after tried a lot of solutions, there is one works!
first, unlock the pixel clock of grahpics card, using:
second, specify your custom resolution using CRU:
Great thanks to the authors of those softwares!!