Steam fails to start and does not generate an error message - what is happening?
Steam may fail to start and silently terminate, or it may continue running in the background without loading the Login dialog.
To determine whether Steam has silently terminated or is still running, please check the Windows Task Manager:
This issue is most commonly caused by a third-party application interfering with Steam. Please see the Programs Which Interfere with Steam topic and the Spyware, Adware, and Viruses Interfering with Steam topic for instructions to ensure any conflicts are resolved.
Please see the Contacting VALVe Billing and Support topic for instructions to contact Steam Support for troubleshooting assistance.