Ok, so I decided to uninstall / reinstall, but this time using the default options for the SQL username and password, BUT....
When I ran the uninstall, it asked me to reboot the server once it had finished.. I'd rather not reboot due to it being our only Domain Controller and I'm going to be installing the same software again anyway, so I chose not to. Now, I know some uninstall programs ask for a restart because they tell Windows to delete previously in-use files while its booting. Obviously I want to avoid this so it doesn't delete needed files...
So what I want to do is find the registry keys and / or files that tells Windows what to delete on boot and remove them accordingly. I've looked in the usual RunOnce and RunOnceEx registry points but they're all empty. Is there anywhere else I should be looking for such things?
Thanks muchly for any help, once again!