nerwork locked and there is no unlock code screen

[AC Question]

I have lg g5 (ls992) and he write me "invalid sim" I check and find out that my phone is "network locked"... I get unlock code (nck, spc, otksl) but I can't get into the unlock code screen and the phone don't open him when I power him on... I try some tricks in the dial screen but neither of them work... any ideas how can I get to the unlock code screen? or unlock the network?