When the vcenter server service is not starting !!

Run the vcenter server service in single user mode when the vcenter server isnt starting all by itself and you are not able to login.
procedure. open a windows command prompt
navigate to the directory of the installation of the vcenter server till you find the vpxd file in the installation directory
ex:-cd c:/progam files/vmware/infrastructure/virtualcenter server/vpxd
run the command
vpxd -s
and observe the errors.