• Read through the ban message you've screenshotted carefully. Follow the (rather simple) instructions in it.
• Have you installed anything dodgy or even a bit suspect recently? Hell, have you ran any executables on your PC recently? If so, your PC may be compromised

and changing your password on that PC is (probably) useless.

• Have you reused your previous password on other websites? Is your password just a few words (with maybe a few numbers added at the end or start, some random capitalization and maybe a few replaced letters)? Is your password short (less than 8 characters)? If any of these are "yes" (especially the first one), there's a possibility the attacker might've just managed to guess it.
• Have you been redirected to a Bitcointalk login screen (or at least what looks like it) via a link in a Bitcointalk PM you've received? If so, someone might've phished you out of your Bitcointalk password.