Operating system in a phone having no OS I have sony xperia P and i was trying to install custom ROM in my phone.I copied the boot.img in the boot partition.Now my phone doesn't starts.

There is no external SD card slot in my phone.

How can i install a android OS now.

My phone starts in fastboot and flashmode.

Any help would be appreciated.

And yes i don't have a backup :(
If you can start your phone in fastboot, then use the fastboot utility to load your system.img and boot.img

You have a nice guide here: http://forum.xda-developers.com/showthread.php?t=2277112 but the main thing you need to execute is:

fastboot flash boot boot.img
fastboot erase system -w
fastboot flash system system.img
fastboot reboot


You will need a valid system.img and boot.img for your phone model.