It also might be prudent to backup your Registry via the Export function in Regedit, in case something goes wrong (like you make a type or something). I would also ensure that your System Restore function is configured and enabled, and also set a Restore Point. These 2 tasks which take only a few minutes, can undo any mistakes you make while making a new entry. Beyond, that, having a Image File backup (such as Macrium, or EASEus) of your hard drive saved to external media can also be a lifesaver in case something gets scrambled in your windows that those 2 undo functions can't restore.
You can also try to use Default Programs association, and change the default launched program for all JPG image files. You should be able to change it from Paint (W7 default) to any other installed Image editing program such as your PSP or another like Paint.net or GIMP.