It's because you have set your default way to open .jar with winrar.
Right click the .jar file and select Open with -> Choose default -> See if you can find Java in the list otherwise there should be a button to browse other programs. Then click that and navigate to C:\Program Files\Java\jre1.8.0_66\bin\javaw.jar
Note that your java version will probably differ from mine which means the jre1.8.0_66 will most likely not have the same numbers as described.
Make sure to select "Always use this program to open this kind of file."
EDIT: Didn't even read the whole thread before posting. Just spent 5 mins to write this shit