不知道从哪里找到的这个方案，反正是能解决了这个问题：

重新升级了CUDA以后，发现在安装CUDA8.0后，分辨率变成800×600，而且不能改变，最终在网上找到了这个方法，运行下面几行代码，然后重启就好了，具体原因还是不是很清楚。

sudo mv /etc/X11/xorg.conf /etc/X11/xorg.conf.backup
sudo touch /etc/X11/xorg.conf
sudo reboot

下面是错误信息，在重新安装完成显卡驱动后，进入桌面，会出现下面的错误：

Could not apply the stored configuration for monitors

none of the selected modes were compatible with the possible modes:
Trying modes for CRTC 63
CRTC 63: trying mode 640x480@60Hz with output at 1366x768@60Hz (pass 0)
CRTC 63: trying mode 640x480@60Hz with output at 1366x768@60Hz (pass 1)
Trying modes for CRTC 64
CRTC 64: trying mode 640x480@60Hz with output at 1366x768@60Hz (pass 0)
CRTC 64: trying mode 640x480@60Hz with output at 1366x768@60Hz (pass 1)
Trying modes for CRTC 65
CRTC 65: trying mode 640x480@60Hz with output at 1366x768@60Hz (pass 0)
CRTC 65: trying mode 640x480@60Hz with output at 1366x768@60Hz (pass 1)
Trying modes for CRTC 66
CRTC 66: trying mode 640x480@60Hz with output at 1366x768@60Hz (pass 0)
CRTC 66: trying mode 640x480@60Hz with output at 1366x768@60Hz (pass 1)