Screen blank when unplugged from monitor

Hi

I have a colleague who has an issue with his Sony Vaio laptop.

When we unplug the laptop from the monitor, the screen on the laptop will not stay on - even though the green power button is on.

When we plug the laptop back in, it does nto synch with the laptop.

We have to reboot to fix either of these issues.

Can anyone help??

Thanks!

Emily