If you downloaded from the internet, I would try uninstalling, then downloading a fresh copy and re-installing. It is possible to sometimes end up with a corrupted download.
Do you have any type of firewire monitor connected to your computer? (such as a dv camcorder, or one of those analog-to-dv conversion boxes) If so, try disconnecing that device before opening up DVDA4. I don't know if it's related, but I had the same issue with Vegas 7 -- it would not open until I disconnected my dv camcorder. I never did track that problem down to see what was causing the issue...