If you open up the Start Menu, right-click inside of the white space in it and select properties. I think that if you un-check the store recently used programs and items boxes then this might clear your Start Menu.
no, it's not pinning. I'm talking about feature which automaticallly puts frequently used programs to start menu.
Right click the program you doesn't want to be showed in the start menu, and click on "Remove from this List." 
So many responses, but only one that answers the question.Is there a way to exclude some programs from automatically showing up in start menu?
To automatically and permanently exclude a program from appearing there:
Registry Key:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\FileAssociation\
To automatically and permanently exclude a program from appearing there:
[Start] [Run] [Regedit]
Registry Key:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\FileAssociation\
In the right pane, double click AddRemoveApps
The [Value Data] box contains a list of the default entries
To add a program to the list, type a semicolon followed by the name of the program executable
Example: To add Notepad, the entry would be ;notepad.exe
Add as many programs as you like and click [OK]
Exit Registry and Reboot
What is the program? Is it seen in 'Services'?
So Opera has decided to make itself your default browser? Have you set your 'default' programs?