Cannot open files and programs in Windows.

Hey guys!
I can’t open files in my windows. I get this error message “Windows even not access to the specified device, path, or file? You may not have the appropriate permissions to access the item” why it comes? I can’t even open my programs like burning software. As I am the administrator of this computer I should have full access to all the programs. But I can’t even setup new antivirus. But I did not lock any option or change any settings of my windows. Help me guys!
