Please help my Lumia 820 not booting up

[Peerawat Dangsupa]

I tried to install new firmware for my lumia 820 then my home's electric is going down when it installing , My phone stuck in installation screen so i put off battery then it not boot anymore but when i connected my phone to pc my pc say it have usb connection but in product support tool it not see any connection. It cannot press volume down + power button too

Please help me to fix it , Thank you and sorry for my bad english

 

[ShreyansShah]

really bad english. try to put some pauses and full stops.
anyway, the only way is to reboot ur phone. try to start by plugging in if ur phone is out of juice.
why r u unable to restart with volume down + power key? u gotta make it work.