I want to sell my PC. I'm going to sell everything but the hard disk. My question is if the motherboard can store some information that have not been removed or not.
The motherboard itself doesn't have any storage to worry about.
But you will have to keep in mind that the Windows license-key is in most cases tied to the motherboard/UEFI/Bios.
So you will be effectively selling the computer + the Windows license and the Windows install (if any) on the hard-disk you have taken out will NOT have a valid Windows license anymore.