Ubuntu: Ubuntu 14.04 - Secondary display not detected after login screen


My computer is an HP zBook 14 with Ubuntu 14.04, 3.18.1 kernel, hybrid graphics display (integrated Intel HD Graphics 4400/discrete AMD FirePro M4100), and the open source drivers. lshw shows I am using the integrated video card:

michael@abrode:~$ sudo lshw -c video  [sudo] password for michael:     *-display                        description: VGA compatible controller         product: Haswell-ULT Integrated Graphics Controller         vendor: Intel Corporation         physical id: 2         bus info: pci@0000:00:02.0         version: 0b         width: 64 bits         clock: 33MHz         capabilities: msi pm vga_controller bus_master cap_list rom         configuration: driver=i915 latency=0         resources: irq:50 memory:d0000000-d03fffff memory:c0000000-cfffffff ioport:4000(size=64)  

Until earlier today, I was able to configure displaying on the laptop screen and an attached secondary monitor. During normal usage, the computer locked up for the first time in about 2 months of usage. I rebooted and at the login screen, the secondary monitor is working (i.e. displays login screen). After logging in, the secondary display is turned off and only the laptop display works. Detecting displays fails to find the connected display. I tried different forms or rebooting with and without the secondary monitor connected to no avail. I also tried booting (via grub) into an older kernel version (3.13), but that did not change behavior.

After logging in, if I switch out of X to the terminal (by default CTRL+ALT+F1), the secondary display mirrors my laptop. This proves it can be recognized and is functional. Switching back to X (by default CTRL+ALT+F7) turns off any display output to the secondary monitor.

Any thoughts on why the secondary monitor works at the login screen but not afterwards? Thank you in advance for any help I can get.

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