I just installed Ubuntu 16.04 on a individual SSD. Windows 10 is pre-install on a separated HD. My video card is AMD Radeon HD 5670 (connected to monitor A) and intel graphic came with the motherboard (connected to monitor B). When I have the monitor B disabled, monitor A works just fine. But when I activate monitor B, then the mouse starts flickering on monitor A and monitor B still shows nothing, except for a few lines left behind from boot up, something says "CPU temperature is over the threshold.

I tried to solve this as suggested in another thread, by deactivating the monitor then activate it. This only works when I'm trying out Ubuntu from the CD/USB. I disable the monitor, then activate, then go into screensaver and wake up the screen. Then magically both monitors work just smoothly.

But this method doesn't work when the system is actually installed. When I disable then reactivate the monitor and go to lock screen, then wake it up and log in, the problem still remains.

However, when I shut down the system, both monitor works normally, showing the Ubuntu icon and the flashing lights beneath.

After reading other threads, I think this might be due to monitor configuration. But I can't locate the files (xorg.conf or monitor.xml) and don't know how to edit it.

Thanks!!!!!!