Touch screen not responding neither working.

I bought a Hisense sero 7 (LE)
I used it for a couple hours and it was working fine.
The tablet suddenly froze at the lock screen and it didn't respond to my touches and didn't sleep when I pressed the lock button. I hard reseted it, went into recovery and factory reseted it. I turned it on and the screen still didn't work. I done that process again, still didn't work.
Can anybody help?

Phone died randomly and now won't power up/charge. Neither LED nor screen turning on.

My phone was running CM12.1 (a week old build). Obviously rooted and runs TWRP.

I texted someone and left my phone with the screen turned off for about an hour. When I tried turning on again, nothing happens. The battery was about 80% the last time I used it.

Things I've tried to get it to work:
1. Charging it with the wall charger. [Nothing happens. LED doesn't turn on, phone doesn't turn on]
2. Plugging it into my PC. [PC doesn't read it. LED/Screen unresponsive]
3. Tried vol down key + power to boot into the bootloader. [No response]
4. Tried vol down key + power, then plugged it into my PC without leaving the buttons and waited for a minute. [No response]

Can anyone explain what the hell went wrong with this? I just use my phone for calls/browsing/texting. Didn't overclock anything. It's been rooted since day 1 (2 years back), and I last installed the CM rom a week ago so it wasn't due to a bad flash.