Unable to log into app store - hanging

Hello!

I recently purchased a second-hand MBP (late 2008, upgraded to 5gb RAM) and have installed OS X El Capitan (10.11.1) on it. Running quite smoothly so far, aside from one issue. When I try to log in to the App Store (no problems with iTunes or anything else), I enter my credentials and go to log in, but upon entry of a correct user/password combination, the loading circle starts turning but never logs me in. Every time this happens, I am having to fore quit to close the store.

Any help with this would be greatly appreciated, thank you!