SQL Server Attach Error 5120

I was trying to attach a mdf file from local backup into Microsoft SQL Server 2012 and I got access denied after clicking OK button. I saw many people was facing this situation. The solution to this problem quite simple, well, at last.  Here’s how:

1. Run your SQL Server Management as Administration
2. Use Windows Authentication
3. Attach your mdf file

I was also trying logged in using SQL Server Authentication but failed. Hopefully, you could then attach your mdf file to SQL Server. Cheers.