Missing VM in ESX 5

Hi,

I have very less knowledge in VMWare. I have created a lab environment with ESX 5.0 o VMWare workstation 8.0 and also created a virtual machine on ESX. But the strange thing is the VM will disappear after reboot. I have created a new VM, but again the same.

Please help me to figure out the issue. I couldnt able to find any blogs related to this issue.

thanks.