When you uninstalled ver 2, did you reboot afterwards?
If you did, and it still didn't work, I would be tempted to try installing PE2 again, reboot, then uninstall again, reboot. Then try to install PE3 again.
Have you looked at adobes website for faqs and/or forum ?s relating to your prob, chances are someone else has had and sorted it.
Hope this helps.