Valve's video game store Steam is currently busted, servers evidently having collapsed a few hours ago. It's extremely common for Steam to collapse at the start of a big sale, though these issues started about 18 hours after the Lunar New Year Sale began so huh, I wonder if that actually is the cause. Whatever it is, hold onto your pennies because we're still waiting for a lasting fix.
Steam seems to have tripped over around noon GMT, with the Store either not loading, giving error messages, or at least taking ages. It seems to struggle back to its feet every so often, then just as I think it's fixed, pow, gone again. Right now, I'm seeing 502 gateway errors.
I've only seen issues with the Store myself, with Friends and games and updates and such still working fine, but evidently it had login issues too. Steam's stats show it suddenly shed over 2 million players around 1:40pm GMT. They seem to be back now? For now, at least.
Anyway. All we can really do is wait for Valve to stabilise things. Until then, why not play Mystery Steam Reviews with Colm and Matthew? If you have sufficient second sight to guess all the games, maybe you'll be able to intuit when Steam will be properly fixed.