When Ubuntu boots, the second monitor mirrors my other monitor, but when the login screen pops up, the monitor doesn't get any signal from my computer. When I go to monitor setup, it is not detected. If I unplug my first monitor, the second works fin with Ubuntu. When I tried 11.10 on a flash drive, it worked fine as a dual monitor. The default seems to be VGA over the DVI connection. Help?
If you have an Nvidia card: install your drivers by opening Additional Drivers and installing the recommended option. Then, try checking out the settings in "nvidia-settings". Go into the Display Configuration category and make sure that neither of your monitors are disabled. If so, change them to TwinView.