I put together a new computer for a friend. Not my first but I am not an expert either. I made it at my place and set it up using my monitor. Everything worked as expected and there was no problem. She took it and hooked it up to her old monitor but the monitor won't work though it works fine with her old PC. Don't think it's an issue with the power supply as neither mine (which works fine) and hers are running the power separately from the computer and it is 750w regardless. Both mine and hers are quite old LCD monitors connected using VGA sockets. Anyone have any idea what the problem may be?