Luckily I found the answer to fix this problem. Here is this solution:
1. Write this line in /etc/modprobe.d/nvidia file (this line has to be on a single line):
options nvidia NVreg_DeviceFileUID=0 NVreg_DeviceFileGID=33 NVreg_DeviceFileMode=0660 NVreg_SoftEDIDs=0 NVreg_Mobile=1
2. Then add this option to the device section of your /etc/X11/xorg.conf:
Option "ConnectedMonitor" "DFP"
Reboot, and everything should be alright...