Login issue

[Ylva]

Sorry for the double thread, fellow mods, but I thought maybe someone here might have ideas!

I recently came back to my flat, so I haven't used that PC for a couple of weeks. When I try to use the LHC on it, I can't post or edit anything. I couldn't even report. It says something about a missing security token.

My Windows is up to date and I cleared my cache and cookies. Now I can't even log in! I input my username and password and click the login button, but it just reloads the page and I'm not logged in. I've cleared the DNS cache and I use the same internet on my PC and phone but phone is connected to WiFi and PC is not wireless. This is posted from my phone. The same happens using a different browser.

I'm at my wits end, any ideas?

ETA: Browsers are also up-to-date