Edit the shortcut to lazarus and add the command line option
--debug-log=c:\laz.log
maybe that will reveal something.
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As for the config of your old install, the new installer can remove it for you. But you must set a checkbox during installation.
Or look in C:\Users\USERNAME\AppData\Local\lazarus
you can backup the folder, and if deleting the content solves the issue, you can restore some of the files.