I also have this problem. I've tried the following: restarting my pc, reinstalling tf2, vertifying game files, resetting my ip, restarting my modem and none of these have fixed the issue. After some research I found out that all of the Stockholm servers are offline for some reason. I also saw a video about the subject that said that it was affecting mainly Russia, Finland and Kazakhstan. I tried talking with Steam support about this and the answer they gave me was nothing short of "Have you tried turning your pc on and off again?". Im not sure if i was even talking to a real human...