Look for a file named *.m12. That would be a copy of your Money 2004 file saved during attempted upgrades. You can copy that or get a copy from your old computer. If you can install and use Money 2004, that would be best. See if you can uninstall Money Sunset, and install Money 2004. Then see if it will create a new file with no password, or better yet, see if you can open a copy of Sample.mny.
Money Sunset will not be able to use your UK Money file. The *.mny file that got produced during the attempted upgrade is not useful.
I don't know whether or not Money 2004 should have worked directly. I was thinking yes. Not sure. If you are going to try a newer version of Money, your only choice is
Money 2005 UK – QFE2