Please follow the steps below to diagnose network connectivity issues within Steam:
Please check the Steam Server Status page to ensure the issue which you are encountering is not related to system-wide downtime. If you encounter any timeout errors when attempting to access Steam sites, it is very likely that there is a system-wide issue and Steam will not be accessible until the issue is resolved.
The Using a Router with Steam topic includes steps to isolate problems if they occur at the router.
Wireless and powerline connections can cause intermittent failures due to interference. If possible, test Steam with a direct wired connection to determine if this is a problem. An Internet speed test may also help you identify problems related to local link quality.
See the Using a Firewall with Steam topic for instructions to test and configure your firewall for Steam.
Note: If you are installing Steam for the first time or Steam has recently been updated, a firewall may be preventing Steam from connecting to the Steam Network - even if Steam worked correctly before the update was applied.
Review the Programs Which May Interfere With Steam and reconfigure, disable or uninstall any programs which may be preventing Steam and Valve games from connecting.
Scan your computer for Spyware, Malware, Adware, or Virus Interfering with Steam.
All required ports to run the Steam application are listed here. It is possible that other games available on Steam will require further ports to be available.
Many university networks and proxies block required ports for Steam operation - please consult your network administrator to ensure the required ports are open if you are using a university network or a proxy. Ports required for Steam can not be re-mapped to HTTP or reconfigured to a custom port range.
If you notice that your Steam connection only has issues during certain hours of the day (for example in the evenings between 5pm and 11pm), it is possible that your ISP is blocking or "shaping" your connection. Please test your connection at other hours of the day and contact your ISP directly if you believe this is causing the connection issue.
Some ISPs have been found to block ports required for the proper operation of Steam and Steam games: