If you have a video card, make sure you are using one of those outputs. If you are using the video card outputs try using a different display port output and I would also try a different cable. If none of that works try a HDMI cable. Also check the settings on the monitor and see if you have that set up correctly. You might have gotten a defective keyboard.
I have not had a desktop in over 10 years. I just got the XPS 8950 with the Ultrasharp U2422H monitor. I believe I am hooking everything up properly but not positive either since it's been so long. When setting up the system, the monitor will not show a picture using the DP cable. It powers on, but will go into standby mode saying no signal detected. I unplugged the DP cable and used a HDMI instead and now it works. Any ideas on the DP cable issue? I tried contacting tech support and after 6 hours was told basically it could be 1 of 3 things and since we aren't sure which they couldn't help. Another issue I am having is the keyboard that came with the computer will not work. On start up, I get a splash screen saying key board initiation failure. It gives an option to continue, bios setup, and diagnostic. I run the diagnostic and it shows pass on everything. I have tried different USB ports and still will not work. However, the USB mouse that came with the computer does work on any of the USB ports.  Am I doing something wrong or does it sound like bad equipment? Thanks
XPS 8950, U2422H, DP not working