Unable to mount system, cache, data and no OS problem in micromax a117.

[AC Question]

I use a micromax magnus A117. I have twrp recovery 2.8.2.0. I was trying to install custom rom so wen i was wiping and swiped to factory reset it shows error Unable to mount /system, unable to mount /data, unable to mount /cache and also i wiped the internal sd card. So now when i install custom rom from external sd card and reboot it says 'No OS installed' and after swiping it is stuck in the logo. How to fix the problem?