In general, 6 beeps is a video card error (Video BIOS Test Failure) on most XPS PC models (excluding XPS 8940). So start by carefully re-seating the video card in its PCI-e slot. And then make sure the video cable is correctly/securely connected to video card and to monitor after you close the case. If the beep code continues, try clearing the error by resetting BIOS:
There is a 6 beeps sound. For one of my Dell computer, I have to keep switching on and off. It takes a few times of switching on and off to boot up. Once the computer is booted up, I can use it for a long period of time without any problem. The problem is that I have to keep switching on and off just to use this computer. Any idea how to solve this? I had disabled the "turn on fast startup" under the power button as recommended by some. But the same problem persists.      
Dell 6 Beeps. Need to restart a few times.