Instead of selecting preview, select "open with", then find the program that you previously used to view that file type. MSPaint, Picture and Fax Viewer, or whatever. You should be given the option to always use that program to view that file type, then Okay your way out and give it a try. If it does not work log out of that user and log back in, or just reboot, then give it a try.
And BTW, didn't you backup the Registry or make a restore point before dinking with the Registry? I know my way around it pretty well, but I still don't forget to backup first. I even document my changes in Outlook Notes which gets backed to my Palm PDA regularly. I have found that some changes to the Registry may have unwanted side effects that do not become apparent until days or weeks longer, when I attempt to do something not done in awhile. By then, or the next day, I have forgotten what I did. If it was a tip I read, I include a link in the note too. Not sure going to that extreme in documenting changes has really helped in the long run, but I have never had to rebuild Windows on this machine since the initial install:
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