There is a known issue on some installations of Yellowfin 7.3
This issues however is easily resolved:
Using the administrator command prompt - navigate to [yellowfin]/appserver/bin
1. remove the yellowfin service.
service remove yellowfin
2. re-add the service
service install yellowfin
3. start the service
service start yellowfin
once started, you can confirm if the service is running by checking
http://[server]:[port]/info.jsp
if this page returns, try logging in
This issue is due to security changes within Windows - we hope to have this resolved in a future Yellowfin version.