First make sure that your system is totally up to date with Microsoft Updates, both critical and non-critical. Make sure that peripherals are up to date too, such as Java (uninstall any older versions), Flash, Shockwave (from Adobe) etc.
Make sure that Internet Explorer is up to date...IE7 if using XP or Vista and under Tools/Internet Options make sure the settings are at default under the Security and Advanced tabs plus the Content Advisor is turned off under the Content tab.
Yes it is always best to uninstall trial software first. Oncce you've installed the boxed product and registered it, there will always be an online link for you to be able to download the latest version of your suite, should the occasion arise. Worlwide download links are listed
here.
Do the following.....
1. Uninstall all McAfee programs through "Add or Remove Programs" in Windows "Control Panel".
2. Use the MCPR tool, see this article:
How to remove supported McAfee consumer products using the McAfee Consumer Products Removal tool (MC... This will remove all McAfee remnants from your computer. (you must have Windows Vista, XP or 2000 SP4 to use this tool)
3. Launch Windows Explorer and delete all McAfee files in "Program Files" but especially in "C:\Document and Settings\<user>\Application Data" and "C:\Document and Settings\All Users\Application Data". You have to set Windows Explorer to show all hidden files and folders (Tools > Folder Options > View tab). Just delete the McAfee folders even if they are empty in all the "Application Data" folders. Can be more than one!
In Vista: C:\Program Files, C:\ProgramData and C:\Users\yourname\AppData\Roaming
If you don't find any files do not worry, This only means that the removal tool did a thorough job.
4. Reboot and redownload/reinstall your McAfee products directly from your account at the McAfee web site, or in your case initially from your boxed set.
If you have any problems registering or reaching your account online it's free to contact Customer Service by phone or chat using the link second from the left at the top of this page.
Technical Support by phone is also free for 30 days in N. America. Chat support is always free of course.