Don't know if this would help at all [since uninstalling didn't work], but in Steam, if you go to the game library and right click Sins, you can go to properties and in there would be a 'verify integrity' option. Though, some other things could be the issue, including any firewalls, odd antivirus behaviors, Steam being Steam [happens to me and TF2 sometimes]... but usually restarting helped me. Sorry, that's all I got.
