Why is my PC monitor so dark?

Why a monitor locks the PC, and when I turn on, the monitor put a sign that says saving power and turn off ?

• My monitor was working good, but I decided to change for a bigger one so, I bought a used one, when I conected to my PC, the PC freezze, I cutted the power and turn on again the monitor, has like a lock after I turn on, after 5 sec, it turn off by itself. I conected my old monitor and happend the same, then I work with the video card and my old monitor works well again; but the first still turning off, even if it is not conected into a PC, just to power happen the same. Why and how can I fix it? Thanks. Please just real answers, not just for get points.

• Answer:

  please check if there is port conflict in your device manager. you forgot to mention if you are using win(version?) or linux so cannot advice further. --------------------------------------… thanks for providing more info. try connecting old monitor and install new monitor drivers. also it could be video card conflict. or your new monitor is bad!