Funny you should post this today. I was asked to help with a similar issue this morning. DB would not come online posting error - insufficient disk space or memory. There was plenty of disc space, but memory was a bit over-taxed. One thing I did note was the ldf was 2+ times larger than the mdf at around 58GB which raises other flags. I ended up doing just this, setting the db offline then online. It took over an hour to come up, but did succeed and we were back in business after doing a little clean-up on the DB.