Can i use two motherboard in one pc??
Possibly, but why?
You would need two power supplies and peripherals.
You could make one MB a slave board with some software with remote access, but unless you describe your application, I think you will find it is better to keep each device separate.
DAB
A regular PC case does not have mounting fasteners for more than one motherboard.
Networking servers have a backplane with multiple slots for SBC cards and a common power supply.
http://thumbs.ebaystatic.com/d/l225/m/mRWtMBVv_vBMTEUmEvJgCMg.jpg
Scott