Another way to reset the preferences for opening files is by right-clicking on the file from an explorer window. Select 'Open with...' (if that option isn't displayed, right-click while holding down 'shift') and select 'Choose program...'. Select the preferred application and tick the box below the list that says 'Always use this program to...'.
Personally I prefer to have JPGs open in the Windows viewer when I double click them. Saves the system loading a heavy application every time I just want to look at a picture. (It is the 'Windows picture and fax viewer' application.) Selecting this program might work better than a third-party application.