it's bricked, you tried to install custom recovery without unlocking bootloader?
you can revive it using that tutorial. leave the battery in in order to get to s/w upgrade screen, but before that, you need drivers (and if your computer isn't detecting it in s/w mode, the drivers aren't installed)
To install custom roms on O4x:
1. upgrade to jb
3. unlock bootloader
4. flash custom recovery (cwm)
5. flash roms
6. if you encounter any issues, search, they've been answered already.
Got issues with RIL/IMEI/BASEBAND on custom 4.2, 4.3 or 4.4 ROMs on p880? Click me for possible solution!