To start with the last question: No, you don't need to install VobSub to display SubRip subtitles (.srt). These are played by BSPlayer natively (without any additional program). In fact a lot of "problems" which are posted on this forum are often caused by other utilities (like VobSub).
Then, with respect to your black screen, you probably havn't the right (up-to-date version of) codec installed. I would first install DivX5.1.1 and see if that solves your black screen.
Click here for a post with a link to DivX5.1.1 codec and others.