If you use Steam Guard blocked all attempts to log in to the Steam account with unauthorized computers, i.e. you can run your account and play it only on one computer. This option is used to reduce the risk of theft of account and purchased games in it.
Update your Steam to the latest available version. Usually update automatically, but you must carry out an additional check using the link "Check for updates" in the program window. To activate Steam Guard, you need to use the newest version of the program.
Confirm tied to your account account e-mail. To do this, click on the "Settings" section. If the address is not confirmed, click on the "checkout" button, and then navigate to the account used email service. Enter the message code in the corresponding field in the Steam client to confirm that you log in to your account.
Restart Steam again and return to the "Settings" section. If the bind operation e-mail was successful, you will see the status "Confirmed" in front line with your email address.
Go to the tab "Account" and select "Manage Steam Guard". Check the box next to "Enable protection" to activate the mode, then press "OK".
Enabling Steam Guard is complete. Now, to go into a Steam account on another computer you must login using your mailbox. When you try to log in from a new device to your account you will receive an email notification with code for a work authorization from the same computer on which you run access.