I found my Lenovo X13 laptop non-functional; after wakeup, it was just cycling through 5 flat color screens displayed on the LCD (red, green, blue, white, etc.) repeatedly. Slight panic...
The service manual (there is such a thing for Lenovo laptops) mentioned pressing
FN + Ctrl + Power to enter the LCD self test (which consists of those cycling color screens). Well, I didn't intend to trigger that test.
Anyway, turning off the system, pressing
FN + Ctrl + Power and the laptop boots normally again. Puuh!