Right click the desktop, and at the bottom of the popup menu, select Screen Resolution. On that screen, make sure it sees the monitor as the Asus VG248Q. If it does, click on the Advanced Settings link on the lower right, and in the panel that comes up, click on the List All Modes. There should be 144Hz options available on that list.
If Windows is not recognizing the monitor as the Asus VG248Q, then there might be a video card or monitor problem that needs to be addressed.
DisplayPort should have no issues running at that resolution and Hz speed. Its been part of the DP standard since 2009.
Something else you might try. If both the video card and monitor have HDMI ports, HDMI since version 1.4 has supported that too. But I did run into someone 2 nights ago that was unable to get a video card with 1.4b to run a 2560x1440@120Hz monitor at anything over 60Hz. I still do not know why, especially since all 1.4 and 2.0 versions of HDMI should support the higher hertz settings.