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I think that your operating system is not cooperating well with your graphics card. You made it work with one monitor, but it broke when you installed the fix for two monitors.
When you boot via recovery mode, will you have dual display, or only one display?
If you have dual display, then try to mimic that way to boot! Otherwise maybe you should try to uninstall the dual display settings.
There are some boot options, that you can see either directly in grub (type 'e' to view and or edit the boot command lines), or in the grub configuration files.
Check the entries in the file
Look for a line similar to
Probably the critical boot option is nomodeset Of course you should not add recovery
linux /boot/vmlinuz-3.2.0-35-generic-pae root=UUID=cdc8b4a7-46af-43bd-91fc-030c21ef9887 ro recovery nomodeset
In the following file
check and change the following line to match what is used in recovery mode
so for example (I don't know about all your boot options)
Finally, run and reboot!