Sorry, but you do not provide very much information for us to go on. We know you are having a problem, but not what exactly that problem is.
What version of Nero do you 'now' have installed on your system?
Can you provide a copy of the Nero log file from a failed write attempt? Remove your serial key before posting.
Did you use the Nero General Clean tool to remove Nero from your system, then download the latest Nero 18.104.22.168 and NeroVision Express 22.214.171.124 and install using your Nero 6 serial key to unlock from Demo mode? If not, please do so.
The more details you can provide, such as step by step process you used, exact steps you took to try and resolve the issues, log files, etc will help us help you.
But what you have provided so far leads me to believe you are not able to install our software from the installation CD, or from a download. And yet you then state you are unable burn. If it's not installing properly, we can not expect it to burn properly.