Default AboutXperia u st25i

Hi all. I'm new here and I dont know where to post this. Sorry about that.
I need some help about Xperia u st25i. It's rooted,bootloader cannot be unlocked but I can enter on recovery mode to install custom roms. I cannot enter on fastboot mode (i've tried everything). I am trying to install cm11. Is there any way to install it or I cannot if bootloader is locked?
Thank you in advance. I really could use some help.
Nobody ?

Sent from my ST25i