I, too, have that same problem with PD 5 not opening. Dafydd was very helpful in a post a couple of weeks ago but we still couldn't figure it out. I emailed support back and forth a few times with my symptoms and came to the conclusion that I had another program that conflicted with PD 5 - and I've decided that it is Pinnacle Studio.
I just couldn't stomach reformatting my hard drive and starting over again. I didn't want to uninstall Studio because I'm still using it and it is working fine. Sooooo . . . . this is how I'm working around the problem.
I have Studio with all my video, audio, stills, etc. installed on my desktop. I also have a laptop that is networked to the desktop. I installed PD 5 on the laptop and "pull" all my content from the desktop. So far, everything is working fine!
I just hope that Cyberlink can find a solution so that their video editing program doesn't conflict with other programs. Even with PD 5 installed, Studio still works fine, so it's got to be a problem with PD 5.
Cindy
PS - Just an FYI . . . I purchased PD 5 within the 30 days of PD 6 being released. I emailed support and they responded that I would be eligible for a free upgrade. However, it's been over a week since they told me they would send me the link, so I hope they will make good on their promise. I am hoping that this new version will not have the program conflicts that PD 5 has - I'm crossing my fingers!