Whenever I try to access the Steam Community Market, it just shows
Error -310 (unknown)
Googling got me nowhere. Has anyone heard of this error/know how to fix it?
Steam's errors usually correspond to HTTP status codes. While there are some that may indicate a problem on your end (like a connection failure or expired authentication) this one is a bit special (it's not usually listed with the "standard" HTTP codes) and means "too many redirects". It hints at a server-side problem, for example a programming mistake.
I realise this is an old post but just in case someone finds this thread with the same question:
I've had this happen on two different occasions while browsing the Steam Store on my desktop application and both times I was able to get around it by searching for the game with the Steam Store on my web browser and after you click play/buy now click the option "Yes, I have steam installed" and it opens steam and downloads just fine.