(Ehh... To be fair I strongly prefer manually writing tags to a text editor/rendering this broken. But that is that. At least the site works for now.)

Okay, so the login/session creation itself indeed works as intended (although if it didn't, then it probably wouldn't work for me, either, let alone in all devices, operating systems and browsers available to me), but your computer for some reason doesn't store or doesn't allow the retrieving of the session key.
 - I asked it before, but what firewall/antivirus do you use (if any, but as it is Windows, I typically assume there is something)? It *shouldn't* interfere, but it is at least possible. (Sorry about pointless little and more than possibly somewhat repetitive questions; save from you giving me long-distance control over your computer I can mostly only guess what might or might not work for you and, well, it can in general be a bit difficult to fix something you cannot even seem to make not function yourself).