Unassociate a program with extension

Whenever I find a .dat, it's associated with Corel WordPerfect and I want to remove that. Please help me do that.

How to Unassociate File Types and Remove File Extension Associations in Windows Vista « My Digital Life

I know the article is for Windows Vista, but Windows 7 and Vista are very similar to each other.

I also have the same problem with .jar format it always opens with notepad.
It seems that the solution you have given is not working for me.
When i type the command and press enter nothing happened.

Have you tried right-clicking the file (Properties) and then changing the type of program it opens with?

Will upload a screenshot (:

Using my step-brothers computer, I'm sorry for any stupid files I use as examples

Found two tutorials on the forums which may be use to both of you:

File Extension Type - Unassociate
Open With - Change Default Program

Hope this helps,

Harry

P.S. Sorry if I am not being of much help

OK that's pretty fair. but i want to make it completely free.
i mean i don't want .jar format to associate with any program.

Do you know some other way to do it.?
Have you tried it? is it working for you?

Ok let me try and tell you.

No dude atleast you are trying and that's enough for me.

The first link supposed to work for me but it dint
Unfortunately the program Shawn suggested don't have the .jar format.
Hope it help sayanb06.
:)Anyway thanks x BlueRobot for trying.

what about making a copy of some random exe (say make a self-extracting archive and leave it on the desktop or use some portable program you have around, or copy an exe from some program you have, does not matter), then you tell the computer to open the file with that, then delete the random exe?

Works if I do it with a jpeg on my machine. after I deleted the thing, the "what you want to open this with?" window appears when I try to open the jpeg.

aakshat said:

The first link supposed to work for me but it dint
Unfortunately the program Shawn suggested don't have the .jar format.
Hope it help sayanb06.
:)Anyway thanks x BlueRobot for trying.

No problem, sorry couldn't help any further, maybe as .jar is a combination of Java class files (or is it .java source files? O.o cant' remember) and not a individual file is the reason why a file extension couldn't be found within the program.