To resolve an issue with a computer not waking up from sleep mode:

1. Unplug the computer from the wall and wait a few minutes.
2. Press and hold the power button for 20 seconds to release any static electricity buildup.
3. Reconnect the power cord and press the power button to turn the computer back on, in case the computer had gone into sleep mode.
4. Check the power settings and adjust the computer sleep settings in order to prevent it from slipping into sleep mode.
5. Replace the computer battery, if the computer is a laptop.