Photo explosion won't start. one day it was working fine the next not at all, I tried unitstalling and reinstaling to no avail

I had the same issue and uninstalled it, cleaned up the registry, re-installed it numerous times and still nothing. Then I changed the compatibility for the .exe to Windows 98/Windows Me even though I am running XP and it started up.

CLEAN INSTALL needed here.
Try uninstalling again, but this time after the uninstall, shut down completely for at least 30 seconds, and then restart.
Then do a search for 'all files and folders' - search for both Photo Explosion and then  OnDemand, with the options "Search system folders", "Search hidden files and folders" and "Search subfolders" checked. Delete all of those files found.
You should do this search and delete whenever you uninstall any programs. It will remove lots and lots of leftover junk files taking up room on your hard drive. It will also give you a "clean install" when you reinstall or install an updated program. (Do this ESPECIALLY when updating to a NEW anti-virus programs and “Internet Security Suite” programs such as McAfee or Norton etc.)
BEFORE RE-INSTALLING Photo Explosion Download and install "Registry Mechanic" then do the updates prior to running it and removing anything for the first time. This will get rid of all your current Registry errors, prior to installing or reinstalling.