Make sure World Wide Web service is started.
Also,if using a firewall, make sure ports are open.
See:
http://resources.arcgis.com/en/help/main/10.1/index.html#//015400000537000000
Even if the Firewall is disabled, make sure port 6080 is open. Also what path are you using to access Web Adaptor. For example:
http://localhost/arcgis/webadaptor
Did you enable SSL? If so, make sure you followed this procedure:
http://resources.arcgis.com/en/help/main/10.1/index.html#/Enabling_SSL_on_ArcGIS_Server_when_accesse...
Even if the Firewall is disabled, make sure port 6080 is open. Also what path are you using to access Web Adaptor. For example:
http://localhost/arcgis/webadaptor
Did you enable SSL? If so, make sure you followed this procedure:
http://resources.arcgis.com/en/help/main/10.1/index.html#/Enabling_SSL_on_ArcGIS_Server_when_accesse...
Check to see if one of these bugs applies:
Bug NIM-087508
Cannot configure ArcGIS Server to use Active Directory as the identity store if the user account provided is restricted from logging onto the Active Directory host.
http://support.esri.com/en/bugs/nimbus/TklNMDg3NTA4
Fixed in 10.2
Bug NIM-087257
Users in a lot of groups cannot authenticate when using HTTPS, ActiveDirectory, and web tier authentication together.
Workaround:
1. Open arcgis/server/framework/runtime/tomcat/conf/server.xml in a text editor.
2. Look for this text at the end of the file:
<Connector SSLEnabled="true" clientAuth="false" keyAlias="SelfSignedCertificate" keystoreFile="/opt/esri/3135_upgrade/arcgis/server/usr/config-store/machines/RHDAILY.ESRI.COM/arcgis.keystore" keystorePass="<blah blah blah>" maxThreads="150" port="6443" protocol="org.apache.coyote.http11.Http11Protocol" scheme="https" secure="true" sslProtocol="TLS"/>
3. Insert maxHttpHeaderSize="65535" as an attribute of the XML so that it looks like this:
<Connector SSLEnabled="true" clientAuth="false" keyAlias="SelfSignedCertificate" keystoreFile="/opt/esri/3135_upgrade/arcgis/server/usr/config-store/machines/RHDAILY.ESRI.COM/arcgis.keystore" keystorePass="<blah blah blah>" maxThreads="150" port="6443" protocol="org.apache.coyote.http11.Http11Protocol" scheme="https" secure="true" sslProtocol="TLS" maxHttpHeaderSize="65535"/>
I did this, and I do not even see this code in the xml file. Should I just copy and paste it? if so, where?