Drop InterVideo an email. They'll get back to you fairly quickly, if my own experience is anything by which one can judge. Tell them how you got your original version of WinDVD and ask them how to get your activation key. I think you just log on with your User ID and Password, then go to a page where you can download the activation key. (This online process has to be done each time the thing is re-installed because the activation key won't work again.)
Sorry, but I've never seen any glitches with the software. What operating system are you running, how much RAM and how much free hard drive space do you have, and what speed is your processor?
Regards,
Jim