In case i want to change the motherboard of my computer without formatting harddisk, Currently there is windows7 is installed, then Is it possible to retain the same licence earlier i had, or i will loss it.
You can't do this with an OEM license (ie if Windows came with the computer when you bought it).
You can do it with a retail license (if you bought Windows separately).
Assuming you have an OEM license for Windows 7 that came with the computer, then you can replace the motherboard with the same model - but you can't upgrade it to a different one.
If you have a retail license, you don't have this restriction.
Yes. According to the Windows 7 EULA, a single license is valid for two processors: