i have same problem, and i try this:
- log In As Administrator on your PC
- log In SQL Server Management Studio as "Windows Aunthication"
- Click Security > Login > choose your login where you want to create DB > right click then Properties > click server roles > then checklist 'dbcreator'.
- Close and log in back with your login account.
This worked for me, and hope will help you.
*sorry for my bad english