Any open documents and applications are moved to the system memory (RAM) and the computer goes to a low-power state. This is similar to pausing a movie DVD. The computer is still powered on, but uses low power. Devices like monitors also use sleep mode to save power consumption.
Why is my monitor entering sleep mode?
Related. Windows computers contain a power-saving feature that will put any connected LCD monitors in sleep mode if they have been inactive for a set period of time.
Why is my monitor not coming out of sleep mode?
Go to “Control Panel -> Power Options,” then select “Change plan settings,” for the power plan you’re currently using, and “Change advanced power settings.” Next, scroll down to “PCI Express,” click the “+” icon next to it, and under “Link State Power Management,” change the setting to “Off” and click “Save changes.”