Steam?

[E.Kilby]

Sometimes if you have an anti-virus software like Mcafee it blocks steam.

Go into your antivirus software>Settings>Disable Firewall.

That what worked when I had this problem.

DO NOT TURN OFF THE FIREWALL.

There's a reason it is there, to protect you against viruses and shit, turning it off makes you vulnerable even if you're very careful with what you do on the internet.
Apologies for sounding like an adult or whatever. I'll edit this post with a guide on how to enable steam if it's blocked

Don't worry I have AVG and mcafee because I put AVG on it and mcaffe cam ready installed so I still have a fire wall up!