I made a reciever using nano and nrf24l01. The ground from esc was connected to battery and the esc bec was powering the nano.
The positive from the battery got directly connected to the antenna of the nrf.
Now two grounds of nano seem to not be connected anymore and its not getting powered from the usb.
I haven't checked the nrf cause i need that nano to check it. Please help 
Sounds likely that you have destroyed the nano and the NRF. Applying 12v to devices meant to run at 5v and 3.3v will do that. Replace the nano and NRF and be more careful next time.
In order for the grounds on the nano to not be connected to eachother (how did you determine this?) traces would have to be burned - you would see scorch marks on the board in this case. I have personally seen traces on a board glow red hot and fuse.
It's also possible that the USB port on the computer was shut down to protect it, or was damaged. Do other things plugged into the USB port work? If the USB port just shut itself down, completely turning the computer off and back on will revive it.
You need to be careful with batteries, particularly large ones and ones with voltage higher than the parts you're working with run off of. Abused lithium batteries can catch fire or explode, and all batteries are capable of providing large amounts of current, making them very capable of damaging things to which they are connected to improperly. Many lithium batteries have short circuit / overcurrent protection (though ones designed for high current, including ones for vapes and some drones do not); other battery chemistries rarely have protection circuits.