There are a few items that can be causing this:
1. The device needs to be powered by the AC Adapter. This vertical line may be indicative of a dead battery or the device loosing power. Powering from the AC adapter will allow you to verify this theory. IF the issue continues it may be a bad power supply, damaged power port on the device, or a LCD connection issue.
- To check the power supply: verify the green light is on and nothing is damaged on the cables or brick itself
- To check the power port: move the input cable a little to see if it sits snuggly or if it moves. If it moves the port may be loose and damaged and might be causing the device to not charge or power on correctly.
2. The issue may be related to a damaged LCD screen or loose input inside of the device. This can be shown by the entire screen not powering on, there being a larger number of black vertical lines. If you move the LCD up, adjusting the height, and down there may also be some flickering that occurs. This would require the device to be returned for repairs and a RMA created.