Question [Q] Xperia U not turning on please help! Flashing went wrong!!

I wanted to unlock my bootloader and install a custom rom but my windows won't recognise the fastboot mode so I started up with linux
I saw tutorials of recoveryX.exe and flashtool which only works for windows so I was searching for a manual way so that I could do it in the terminal ..

so I found some tutorial online which told me to flash some file something like

fastboot flash boot xyz.inf I don't remember the extension perfectly but it wasn't a zip or an img ..
and after that my phone turned off, I can still go for fastboot mode but I don't see anything on the screen please help me

I do not have windows so I cannot use flashtool or recoveryX.exe