Troubleshooting Vcenter issues

Vcenter Service VPXD  is the main services  that should run for the Vcenter to function properly.

Location of config files and logs in Win2008:
C:\programdata\Vmware\VmwareVirtualCenter\vpxd.cfg
C:\programdata\Vmware\VmwareVirtualCenter\logs

1) Make sure VPXD services in Vcenter is started.
2) Look for the credentials used for VPXD are  correct
3)Verify the Hostname or IP of the Database changed
4)Vcenter Database name changed
5)Username and Password changed for database
6)DSN changed (Data Source Name)
7)Verify type of DSN (32 or 64 bit)
8)Check the port 80,443,906 on Vcenter if they are used by some other services
9)Out of space on SQL servers or DB

Referrences :
Refer Vmware KB articles 1003979 & 1003928 & 1003926

Notes :-
netstat -an | more to check all listening ports
TCPVIEW from MS sysinternals to view all the ports with names.