Default E975 no signal and restart after 1 minute working!

Hello friends,
I've install CARBON 4.4.2 ROM on my LG E975 after that when camera force closed I restart phone, but it didn't boot up! Then I try flash another rom but any rom didn't boot up at all except official CM11, but it didn't detect sim card! So I decide to flash official KDZ with flash tool, after flashing KDZ it boots up but still didn't have signal and also IMEI is unknown!
As I checked it seems the baseband problem and unfortunately I don't have backup of my EFS partition
First I want to know is it baseband issue and where can I find E975 baseband and how to flash when bootloader is locked?!

Another strange issue is that after flashing KDZ when I turn on phone, It works but restarts after 1 min and it repeats...!! What is this problem for?

Thank you all in advance