'Open' No Longer Default when Double Clicking My Computer, Folders

[KapaKai5O]

When it rains, it seems to pour! Or perhaps I've entered the IT Twilight Zone?
Today, out of the blue, when I double click 'My Computer', any folder, and most links (Control Panel links etc.), instead of said objects opening normally, another program that has set itself into the context menu opens instead.

Because for some unknown reason, and unlike every other system, opening that program is now the default action?!

In other words, this program (which is on all my computers) mysteriously replaced 'Open' as default action on this one system.
Where 'Open' used to be on the top of the right-click menu, this program has now taken that spot.
I can however, right-click every one of these objects and choose 'Open' and they all open normally.
I've got this same setup on other computers and this hasn't happened.

Though I've never experienced this on my own systems, I HAD notes on how to fix this in XP, 2003 and earlier, but I'm unable to get to them at the moment.

I've only started working with W7, so I'm not sure where to begin, but as I recall, it should be a simple registry fix.

I have setup custom context menus items that I don't want to mess up.
Can I somehow simply make 'Open' the default action without messing with existing context menus?

Thank you for any help - Any minute I'm expecting Rod Serling to walk through my door.

 

[BisVal]

go to command prompt and write this command:
cd\
c:\> attrib -r -h -s autorun.inf
c:\> del autorun.inf
d:\> attrib -r -h -s autorun.inf
d:\> del autorun.inf
restart the pc

c and d reffers to the letters of partitions you have on your HD , if there is more - execute for everyone

 

[KapaKai5O]

go to command prompt and write this command:
cd\
c:\> attrib -r -h -s autorun.inf
c:\> del autorun.inf
d:\> attrib -r -h -s autorun.inf
d:\> del autorun.inf
restart the pc

c and d reffers to the letters of partitions you have on your HD , if there is more - execute for everyone

Thanks BisVal!
I remembered I'd Imaged system before all this happened. Only minor changes since which i can redo.

However, this is very interesting. I remember doing something similar eons ago with NT.
It's been so long ago I forgot why I implemented it and what it does. Looks like it will remove
read only, hidden & system attributes from files but don't know how the autorun.inf fits. It's been that long.
I'll give it a whirl but if there's still something amiss, I'll restore latest and go from there.

I just can't get over how many people have this problem. In my case, it just came out of nowhere.

I also came across this:

http://www.winhelponline.com/blog/file-asso-fixes-for-windows-7/

Thank You Again!