Is your main ACP showing any error notifications at the top of the screen (where you saw the template merge issue).
You can enter a ticket and get some assistance, but I'm pretty sure it's going to be a template/style issue.
What is the link to the site?
If you don't want to enter a ticket, you can start a convo with me and I can take a look at it for you.
The master rebuild "resets" the templates. There is no "reset" key per-se. You might be able to set it up as a new forum and merge your old one (haven't done that myself and @Brogan could advise if possible).
I only had two styles "default" and the custom one. I thought enabling "Default" was all i had to do, unfortunately i was wrong and wasted your time...sorry. I am still having an issue with getting FURLS working. I have tried the steps suggested in the FAQS but they dont seem to work for me.