I accidentally deleted everything from Sony Xperia P I has Sony Xperia P(Rooted and Bootloader Unlocked) and I followed this tutorial to install Android 5.0.2 lollipop on it: Installation Tutorial, everything was running well, but after one weak, I accidentally deleted System Files, Dalvik Cache and other system files from it, I can't restore it, when I turn it on, I see only Xperia logo on the screen.

Please help, how to add files on it and install new OS?
Simply, follow the steps from the link you posted, if you already tried that but still same, you can always flash the stock ftf file for your phone using flashtool, and then you can install cm12 again if you want with the same steps, 


  Sony Xperia P LT22i FTF: Download #4.1.2
  
  Flashtool: Download     #latest version
  
  Guide for using FT: HERE