[Q] HTC one wont boot with softkeys glowing topic

hi Guys, i dont know if i m posting in right thread. I encountered this issue lately. while i was listen to music through headphone, i opened the application called Audio Fx or something like that ( CM 12 latest nightly Android lollipop ) screen of my set suddenly turned off, blanked along with music stopped. Now the phone isn't responding at all. the soft keys ( Home key and Arrow key ) of the phone are glowing continuously . Whereas. battery prior to this was almost 82 percent.

I have tried following things;

1. Tried to press and hold power button while holding volume down button for several seconds ( nothing happened )
2. Tried to press and hold power button while holding volume up button for several seconds ( nothing happened )
3. Tried to press and hold power button and pressing the Volume up and Down buttons simultaneously for about 2 minutes while phone was connecting to power source.

while i connect to power source i.e. charger, no LED light is observable either Red or Green.

I would you guys to please help me out

HTC One M7
Android 5.0.1 Lollipop Custom Rom CM 12 nighties dated 27/02/2015
TWRP recovery.