SOLVED! No software issues. I didn't realize everything was due to the faulty volume button. No VOL- means I couldn't get to FASTBOOT and back to MIUI. Phone is as new. At least I'm a pro at booting now :P If you have the same issue, make sure you can get to FASTBOOT. If you can't, it could possibly be due to hardware issues - in my case it was the VOL(-) button that wasn't working. Power + VOL(+) brings you to Recovery mode, Power + VOL(-) to FASTBOOT.