unable to open the physical file mdf operating system error access is denied

Solution:

Steps are given bellow:

• go to Control Panel ->
• System and Security ->
• Administrative Tools ->
• Services ->
• Double Click SQL Server (SQLEXPRESS) -> right click, Properties
• Select Log On Tab
• Select "Local System Account" (the default was some obtuse Windows System account)
• -> OK
• right click, Stop
• right click, Start

Now you want to try attach your .mdf file.