I don't have backup files. I downloaded it from Roxio and thought I could come back to the website to redownload. No?
Um . . . . NO, I don't think so. I haven't found anywhere on the Roxio site where you can re-download purchased software.
Corel sells their Roxio software downloads through a company called Digital River, and if you haven't kept a copy you would have to try to get a second download from Digital River. A good place to start would be to try the download link they sent you when you first bought the software.
If that's no longer active (which is very probable) approach Digital River with your Order Number - you did keep that, didn't you? - and see  if they still have a copy of NXT Pro 4, and  if they will let you have another copy.
Once you have a copy of the software, run it and select the Repair option when it is offered. That should go through your installation and repair the part(s) which have failed. A repair does not subtract from the limited number of installs your serial number key is allowed.
If a Repair doesn't fix the problem your remaining option is to Reinstall. That's not such a good option because you must have the Internet connected, and every attempt to install is counted at Roxio.com. When you reach the limit they allow, your key becomes useless unless you can get Roxio Support to re-set it.
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