QTP install issue

I installed a trial version of QTP of my system. But it asked for trial installation key. I contacted HP and they gave me one which was actually the concurrent license key. And when I tried to install using that key. I was able to install but not able to open the application as it would show up an error. Again I contacted them and they told me that i need to install with single user key and this time they gave a single user key. But when I try to install with the single user again there is an error and this time it "says the data has been modified on my windows operation system. Therefore the demo license expired". When talked with the rep he is telling that I need to clean up the system to fix the registry problems. I did clean up the registry. I am not sure how should I handle this issue. How do I clean up the system for fixing the registry issues? I haven't used the application even once before this or changed any OS dates. Please please help.