I got it working again on my user's laptop. I uninstalled Spark, the deleted the entire c:\users\username\appdata\roaming\spark folder. Then removed all spark registry keys from the registry (backed it up first). I didn't have enough time to look into if there was specific file in the c:\users\username\appdata\roaming\spark folder causing an issue.
Re installed Spark and it is now working - version 2.6.3