custom os problem with the phone

I got a warning that download custom os for u r apps protection, otherwise it may cause danger to u r phone.there are 2 options

volume up: for continue

volume down :for cancle

i choosed volume up then just andorid symbol came, saying that "don't turn off the target" whole nigth it was showing the same thing.

suddenly in the morning the screen was blank

its not getting on.i have done all the things to turn it on. but it does not plz say me the problem and solution to it plz...