VC going down should not in any way cause your VM's to be shutdown. What version of ESX are you running? Are you using auto startups/shutdowns? Can you ping your VM's when VC is down? You should be able to since they are running on ESX and not dependent on VC. Anyone else have access to VC/ESX that may be shutting them down? I'd start withe the log file and see what they say.
How do I troubleshoot ESX server issues?
• You can check several log files on the ESX server based on the problem you are experiencing, these include:
o Vmkernel - /var/log/vmkernel – records activities related to the virtual machines and ESX server
o Vmkernel Warnings - /var/log/vmkwarning – records activities with the virtual machines
o Vmkernel Summary - /var/log/vmksummary - Used to determine uptime and availability statistics for ESX Server; human-readable summary found in /var/log/vmksummary.txt
o ESX Server host agent log - /var/log/vmware/hostd.log - Contains information on the agent that manages and configures the ESX Server host and its virtual machines (Search the file date/time stamps to find the log file it is currently outputting to.)
o Service Console - /var/log/messages - Contain all general log messages used to troubleshoot virtual machines or ESX Server
o Web Access - /var/log/vmware/webAccess - Records information on Web-based access to ESX Server
o Authentication log - /var/log/secure - Contains records of connections that require authentication, such as VMware daemons and actions initiated by the xinetd daemon.
o VirtualCenter agent - /var/log/vmware/vpx - Contains information on the agent that communicates with VirtualCenter
o Virtual Machines - The same directory as the affected virtual machine’s configuration files; named vmware.log - Contain information when a virtual machine crashes or ends abnormally
How do I troubleshoot VirtualCenter server issues?
o To troubleshoot Virtual Center problems click on the Admin button in Virtual Center and then click the System Logs tab
o To view the log files directly open Windows Explorer and go to the C:\Windows\Temp\VPX directory on the Virtual Center server
