Vertical lines on a screen - Toshiba Computers & Internet

If the image is ok on an external monitor it
Could be a failing screen, or loose VGA cable
Remove the screen bezel and the hinges that hold the screen onto the lid, check that the vga cable is tight in the connector, check also that the inverter cable is secure and the lead from the motherboard to the other end of the inverter cable is tight.

Check if possible that the other end of the vga cable that goes to the motherboard has not worked loose.

If these are tight, the screen is beginning to fail and will need replacing
If you get the same problem on another external monitor, the problem lies in the graphics chip, sometimes , this is a sign of overheating, you should strip the laptop and clean out the fan and heatsink assembly