All programs open with notepad

Hi friends,
I am facing one big problem. Whenever i try to open any file, it opens in notepad automatically. I don't understand what's going wrong. Can someone help me with this?

All suggestions are welcome.

Try following:

• Right click on the file which you want to open
• Go to Properties
• Click the change button to change the type of file
• Click apply and OK

If you want to open any image file change it to bitmap file type.

I think your system has virus infections. Update your antivirus and rum system scan. Delete any infections if detected. Run applications for malware and spyware.
When you double-click an .EXE file, the program may not launch, instead it may open in Notepad (displaying the .exe contents).

When you open any file (with .dat extension) in open with option, that time if you checked the box "Always use the selected program" as notepad. It may be possible that because of this, all files are opening in notepad.

Is there any other way to revert back to the old settings rather than changing each association ?