No longer able to access remote folder.

One time I canceled a login because I was on an incompatible VPN and it stalled. Since then, whenever I open WinSCP it doesn't prompt me to log in to access the remote host. I don't see any option to pull it up – both panes show me directories in my own computer. I've reopened the application several times with no change.

It looks like you have disabled automatic Login dialog popup by mistake.
Re-enable it here:
https://winscp.net/eng/docs/ui_pref_window
Or just open it manually:
https://winscp.net/eng/docs/task_connections#opening_additional_connection

See also WinSCP suddenly opens with two local panels with seemingly no option to open a connection to my server. What do I do?.