Blue Iris

My blue iris has been running fine for a couple years now until today. All of a sudden it's playing up, hanging and freezing. I restarted the PC to no avail, tried repairing the downloaded file. In the end I figured it was because I needed to pay for another year and so that's what I've done only now it freezes *and* written across the cameras is "Blue iris evaluation version". How can it be an evaluation version when I put the key in showing I paid?

Are you attempting to upgrade from 4 to 5? If so, see this 4 -> 5 migration guide:
https://ipcamtalk.com/threads/blue-iris ... ide.39211/

Your product key is only good for versions up to the licensed period (typically a year from purchase). If you manually download a version newer than your licensed support period, the Blue Iris will go into Demo mode just as if you didn't enter a license key. Either purchase a support extension ($34.95 for 1 year at a time, or $29.95/yr recurring as of this writing), or downgrade back to a version released within your licensed support period to make the evaluation message go away.

You might consider reviewing Performance and Troubleshooting - Software Startup Issues. BI registration info is stored in the registry. Also, you didn't distinguish whether or not you were upgrading from 4 -> 5 or just renewing your support license.

If you've upgraded versions, see the Blue Iris 4 to 5 Migration Guide