Re: I can't see my forum!!
You don’t need to revert your permalink – you don’t need to even change them.
When you go to Settings > Permalinks, simply loading that page triggers permalinks to be flushed.
As to why it won’t work with pretty permalinks, it could be a combination of things really. Does *any* part of the forum work with pretty permalinks? Does the rest of your site work OK with pretty permalinks?