Easiest route is probably upgrading or re-installing the Java Runtime Environment (JRE).
Or this:
- Open the Windows Explorer, from the Tools select ‘Folder Options…’
- Click the File Types tab, scroll down and select JAR File type.
- Press the Advanced button.
- In the Edit File Type dialog box, select open in Actions box and click Edit…
- Press the Browse button and navigate to the location the Java interpreter javaw.exe.
- In the Application used to perform action field, needs to display something similar to
C:\Program Files\Java\j2re1.4.2_04\bin\javaw.exe" -jar "%1" %(Note: the part starting with ‘javaw’ must be exactly like that; the other part of the path name can vary depending on which version of Java you’re using) then press the OK buttons until all the dialogs are closed.