If you're seeing this dialog, it means that a key component of Steam failed to initialize. Following is more information on the options offered to you when this problem occurs.

Restart Steam

Frequently this issue can be resolved by simply restarting Steam.

Restart steamwebhelper

Attempt to restart only the rendering components of Steam.

Check whether third party software is interfering with Steam

Some third party applications, like anti-virus/security software have been known to potentially cause issues with Steam, resulting in hangs or crashes. Please see our article on Programs Which May Interfere with Steam for more information.