Do you have Dreamweaver 8 (might happen in MX or MX2004 as well)? Open up a CSS file (make sure all your other files are saved).
Make a few rules in the file. Now right before the closing } on one of your rules, add an apostrophe ( ‘ ), and hit save.
If your setup is anything like mine, you should see Dreamweaver disappear, and you cant get it open again. Nice, Macromedia. Real nice.
Anyways, to get it to where you CAN open DW again, open that CSS file and remove the offending apostrophe.
I have no idea why this happens, but it sent me for a 10 minute loop.