A few days ago, I was browsing questions on Mathematics Stack Exchange on Ubuntu 14.04 LTS. I opened lots of tabs in Google Chromium. Suddenly, the screen went grey. I don’t know the cause. I hadn’t seen such problem before. I waited for about one minute, and I switched to the terminal tty3. The grey screen became black without any text. I pressed <Ctrl>-<Alt>-<F7>, then the monitor showed the grey screen again.

I looked at the light (not the power button) in the desktop. I thought it represented the hard disk activity. Its blinking was normal. As a result, I guessed the problem was related to the display. I pretended I could normally see things, and I imagined the picture. I logged on tty3 without logging off tty7. Then I typed sudo reboot and supplied the password. Within several seconds, I heard a beep sound and the system rebooted.

Certainly, all unsaved works on tty7 had been lost. Therefore, it was very important to save your work. As I’m no longer an IT worker, I won’t try to find a solution after reading a few related posts which I have difficulty to understand. Within six months, a new LTS version of Ubuntu will be launched. The price of a SSD will drop, so perhaps I will clean install Ubuntu on a SSD.