why my phone's screen stuck on samsung galaxy logo?

[Himanshu2275]

first i had root my phone to install dolby atmos.after root i tried to flash twrp recovry software but it did not flash completely than i reboot my phone through quick reboot software and than my phone's screen stuck on samsung galaxy logo with a exclamation mark in the upper left corner of the screen..no command works now ..no manual command works..what work is just cutom rom installation command that is volume down +home + power button.my phone is samsung galaxy star 2. And my PC is unable to detect my phone via USB.