Make sure Steam is not blocked by the firewall. (?)
Back up your game content files and reinstall?
Mac or Windows?I had this problem on my mac.I dunno how to do it on Windows, but find where your computer stores data (%appdata% or something) and delete the steam folder. Should work
restart computer?
Is your computer turned on?
I don't think that will fix it considering there will be NO STEAM TO RUN.