There is a problem with the with HA in VMware ESX 3.5 Update 3. Virtual Machines may reboot unexpectedly when migrated with VMotion or after a Power On operation. This is only when the Virtual Machine is running on an ESX 3.5 Update 3 Host and the ESX Host has VMware HA enabled with "Virtual Machine Monitoring" option active.To work around this problem: 

Option 1: Disable Virtual Machine Monitoring

1.     Select the VMware HA cluster and choose Edit Settings from the right-click menu.

2.     In the Cluster Settings dialog box, select VMware HA in the left column.

3.     Un-Check the Enable virtual machine monitoring check box.

4.     Click OK.

Option 2: Set hostd hearbeat delay to 0

1.     Disconnect the host from VC (Right click on host in VI Client and select "Disconnect" )

2.     Login as root to the ESX Server with SSH.

3.     Using a text editor such as nano or vi, edit the file /etc/vmware/hostd/config.xml

4.     Set the "heartbeatDelayInSecs" tag under "vmsvc" to 0 seconds as shown here:

<vmsvc>
     <heartbeatDelayInSecs>0</heartbeatDelayInSecs>
     <enabled>true</enabled>
</vmsvc>

5.     Restart the management agents for this change to take effect.

service mgmt-vmware restart

6.     Reconnect the host in VC ( Right click on host in VI Client and select "Connect" )