I installed a build agent on Windows 7 and always have the agent show up as "disconnected". The log teamcity-agent.txt shows below information
If this is the first time this agent registered on the server make sure it is authorized by administrator in the server web UI.
[2012-09-05 02:56:14,416] INFO - jetbrains.buildServer.AGENT - Agent registration finished.
[2012-09-05 02:56:14,418] INFO - jetbrains.buildServer.AGENT - Stop command was not performed. No build to stop with reason: BuildInterruptReason.AGENT_SHUTDOWN
[2012-09-05 02:56:14,418] INFO - jetbrains.buildServer.AGENT - Starting agent shutdown sequence, reason: Restart agent, failed to download upgrade from server
[2012-09-05 02:56:14,424] INFO - jetbrains.buildServer.AGENT - Host configuration for downloading updates: HostConfiguration[host=http://myteamcity:8080]
[2012-09-05 02:56:14,424] INFO - jetbrains.buildServer.AGENT - Downloading http://myteamcity:8080/update/teamcity-agent.xml ==> C:\BuildAgent\temp\iQ0fjie6zR125neulJeqiYauT8zQ5zOI
[2012-09-05 02:56:15,070] INFO - jetbrains.buildServer.AGENT - Downloading http://myteamcity:8080/update/plugins/agentSystemInfo.zip ==> C:\BuildAgent\update\plugins\agentSystemInfo.zip
[2012-09-05 02:56:15,747] INFO - jetbrains.buildServer.AGENT - Downloading http://myteamcity:8080/update/plugins/amazonEC2.zip ==> C:\BuildAgent\update\plugins\amazonEC2.zip
[2012-09-05 02:56:16,617] INFO - agent.impl.AgentPortFileWriter - Delete agent runtime file from C:\BuildAgent\logs\buildAgent.port
[2012-09-05 02:56:16,619] INFO - jetbrains.buildServer.AGENT - Unregistering from build server: 18
[2012-09-05 02:56:16,800] INFO - jetbrains.buildServer.AGENT - Shutdown agent WebServer start
[2012-09-05 02:56:16,801] INFO - jetbrains.buildServer.AGENT - Shutdown agent WebServer finish
[2012-09-05 02:56:16,801] INFO - jetbrains.buildServer.AGENT - Shutdown agent finish
[2012-09-05 02:56:16,968] INFO - jetbrains.buildServer.AGENT - Downloading http://myteamcity:8080/update/plugins/ant.zip ==> C:\BuildAgent\update\plugins\ant.zip
[2012-09-05 02:56:50,086] INFO - jetbrains.buildServer.AGENT - Downloading http://myteamcity:8080/update/plugins/antPlugin.zip ==> C:\BuildAgent\update\plugins\antPlugin.zip
[2012-09-05 02:56:52,070] INFO - jetbrains.buildServer.AGENT - Downloading http://myteamcity:8080/update/plugins/assembly-info-patcher.zip ==> C:\BuildAgent\update\plugins\assembly-info-patcher.zip
[2012-09-05 02:56:53,464] INFO - jetbrains.buildServer.AGENT - Downloading http://myteamcity:8080/update/plugins/clearcase-agent.zip ==> C:\BuildAgent\update\plugins\clearcase-agent.zip
[2012-09-05 02:56:55,375] INFO - jetbrains.buildServer.AGENT - Downloading http://myteamcity:8080/update/plugins/cmake-runner.zip ==> C:\BuildAgent\update\plugins\cmake-runner.zip
[2012-09-05 02:56:57,190] INFO - jetbrains.buildServer.AGENT - Downloading http://myteamcity:8080/update/plugins/commandLineRunner.jar ==> C:\BuildAgent\update\plugins\commandLineRunner.jar
[2012-09-05 02:56:58,218] INFO - jetbrains.buildServer.AGENT - Downloading http://myteamcity:8080/update/plugins/coveragePlugin.zip ==> C:\BuildAgent\update\plugins\coveragePlugin.zip
[2012-09-05 02:57:11,629] INFO - jetbrains.buildServer.AGENT - Downloading http://myteamcity:8080/update/plugins/crashDetector.zip ==> C:\BuildAgent\update\plugins\crashDetector.zip
[2012-09-05 02:57:12,436] INFO - jetbrains.buildServer.AGENT - Downloading http://myteamcity:8080/update/plugins/cvsAgent.zip ==> C:\BuildAgent\update\plugins\cvsAgent.zip
[2012-09-05 02:57:20,720] INFO - jetbrains.buildServer.AGENT - Downloading http://myteamcity:8080/update/plugins/dotCover.zip ==> C:\BuildAgent\update\plugins\dotCover.zip
[2012-09-05 02:58:00,011] INFO - jetbrains.buildServer.AGENT - Downloading http://myteamcity:8080/update/plugins/dotNetPlugin.zip ==> C:\BuildAgent\update\plugins\dotNetPlugin.zip
How can I get the agent connected?
Here is a very comprehensive blog on re-connecting disconnected agents
http://michaelbarnesjr.wordpress.com/2012/10/18/teamcity-build-agent-disconnected/
Here are the steps (copied from the above link)
If an agent becomes disconnected for whatever reason, you can follow these steps to re-connect it:
That will start the agent, and after a few seconds or so, the next time you go to TeamCity, it will be connected.
If Team City is running on a windows server, you can connect to that server, go to Services and restart the build agent that has become disconnected.