Basics Trouble shooting on VMware ESX/ESXi

1) What is management service service used for ESX/ESXi Server?
2) What is Watchdog ?
3) What is Host Agent ?

I am not able to create the VM's in  running ESX / ESXi Server, But i have some VM in ESX Server which is Running with out Any issue .

How to Solve this issue ?
[root@server]# service mgmt-vmware restart
Stopping VMware ESX Server Management services:
VMware ESX Server Host Agent Watchdog [ OK ]
VMware ESX Server Host Agent [ OK ]
Starting VMware ESX Server Management services:
VMware ESX Server Host Agent (background) [ OK ]
Availability report startup (background) [ OK ]
[root@server]# service vmware-vpxa restart
Stopping vmware-vpxa: [ OK ]
Starting vmware-vpxa: [ OK ]
[root@server]#