Go to the BIOS screen, if the problem shows up in the bios, it is the monitor. If it does not, then it is the computer. Most likey the video card.
If it is the computer, check video setting, try enabling VGA mode, do a power drain on the computer. Uninstall and resintall the display adapter. Look for update.
If it is the monitor, do a power drain. Reseat the setting to factory. If that does not fix it, I would change the monitor. Hopefully helps you.