htc 820g won't go on unless plugged then it goes off again

[Ea_felshenety]

So I woke up today to my htc desire 820G all good and fully charged checked the time, unplugged it and locked the screen. 5 minutes later I tried to unlock and check the time but found my phone turned off so I turned it back on it worked for less than an hour then
started to go off whenever I locked the screen and tried to unlock it again it doesn't unlock it just starts up as if I turned off
It kept doing that for almost 5 hours, when I plugged it in it started charging even though it was fully charged I turned it on and then it immediately went off.
about an hour later I tried to turn it on, it wouldnt even turn on.
whenever I plug it in it starts charging but as soon as I turn it on it goes off after the HTC startup screen displays
and now it won't even go on and I have no idea what happened
and I need it to function because it has all my work credentials and details
Can anyone please help me?

gotta admit tho, I drop my phone often on the floor but it used to workout fine.

PS
Also, the software is not the same as when I first got the phone I had to reinstall it after my phone caught malware and i had no access to my phone and eversince the phone got really slow and sometimes it does not process sounds properly and it comes out as noise

 

[webworkings]

What software is the phone running now and what was it running before?