Troubleshootinghttp://www.electricmonk.org.uk/category/certification/vcap5-dca/objective-6-advanced-troubleshooting/

Points to think about

Check Network Connectivity
Check Storage Connectivity
Check vCenter Connectivity
Check Host Connectivity
Check VM Connectivity
Check Host Logs
Check vCenter Logs
Check Monitoring Systems
Check Physical Switches
Check Cables
Check Virtual Switches
Check FC Switches
Check SAN Storage
Check vCenter DB Connectivity
Check Router Connectivity
Check Power Issues
Check KB Articles for Error IDs

http://www.electricmonk.org.uk/category/certification/vcap5-dca/objective-6-advanced-troubleshooting/

 DCUI,

• Configure Root password
• Configure Lockdown mode
• Configure Management network
• Restart Management Network
• Test or disable Management
• Configure Keyboard
• View Support Information
• View System Logs
• Restart Management Network
• Reset System Configuration
• Remove Custom Extensions
• Shutdown or Restart /Reboot the ESXi Server

Firewall Ports to check

The following ports are enabled by default. If your port is not listed, you may need to enable a pre-defined rule or setup a custom firewall rule