User login screen not responding

Macbook Pro 2011. El Capitan.

It all started when my external HDD was "read only".

I have two HDD. One for time machine only, the other for files. The HDD for time machine worked fine. I could see the permissions and it allowed read and write. The problematic one, under permissions, it said "You can only read".

It was the first time I touched my laptop and external HDD after about 3 weeks of being away and leaving the laptop at home. I backed up the week before I left so it couldn't have been something I did. Disk utility didn't help. I couldn't click First Aid or Verify disk. So I tried my luck at restarting my mbp. But when it got to the login screen (where I'm supposed to choose my account or guest user), the mouse moves as I touched the trackpad but clicking does nothing. The login screen does nothing.

I tried restarting NVAM or something that involves pressing cmd+option+p+r and waiting for three restarts. Same thing. Login screen doesn't respond. I tried starting in safe mode (pressing shift after hearing the startup sound). Same thing again. The screen shows I'm in safe mode and on the user login screen. Pressing the enter/return key just causes a white flash on the screen. 30 min later and it's still not responding.