Default [Q] Screen Won't Turn On; Everything Else Functions Properly

I am/was having an interesting problem with my SPH-L710. I was recently at the gym listening to music on my phone, and it was functioning normally. I took my phone out of my pocket and pushed the power button, but the screen wouldn't turn on. The music was still playing, so I knew that my phone didn't just freeze. There was no immediate cause for my phone to stop working (ie I didn't drop it or get it wet at the gym), although I've dropped it several times before today without incident.

I took the battery out of the phone for a few minutes and restarted my phone. The phone turned on normally except the screen wouldn't turn on. I called myself from my landline and used the normal gesture to answer my phone and confirmed that I'm able to receive phone calls and that touch controls are working. I also tried booting my phone into both the recovery and ODIN download screens. I'm not sure if I successfully booted into those modes, but I do know that my screen didn't turn on when I tried to boot into those modes.

I took the SD card out of my phone and activated my backup phone through the Sprint website. I tried resetting my SPH-L710 after deactivating it, and the screen was functioning again. I reactivated my SPH-L710, and now it appears to be functioning normally. I have no idea whether taking the SD card out or deactivating my phone actually solved my problem or if it was just coincidence.

My ROM is MD4 with root. I have Team Win Recovery Project v2.5.0.0. My phone has been nagging me to install 4.3 for a few months now, but I haven't gotten around to researching updated ROMs yet.

My phone now appears to be functioning normally. Has anybody experienced anything like this before?