Are you using Google Chrome?
Another member had the same (or rather similar issue) last week and we could apparently solve it by logging out, clearing the browser cache (history, cookies, stored website data etc., minus saved access info), and it worked fine after that.
Given that I don't have any issues with various other browsers on different devices, I suspect it might be to do with a recent Google Chrome update.
In any case, I would suggest clearing your browser cache, restarting the browser, then re-loading the forum start page (using ctrl-F5 on a PC-based browser for a hard refresh), and chances should be that should do it. If it doesn't, please reply to this thread with non-personal info such as OS and browser used.