This can be caused by improper shut down of the virtual machine, system crash or unstable power supply. File system or any other system file may have become corrupted.
0) Make a backup of the virtual machine, even though it does not start. Copy the .PVM file (/User/Documents/Parallels/VM_NAME.pvm) to any safe location.
1) First step is to check the .hdd file size (VM_NAME.pvm > VM_NAME.hdd), in case it remains the same you may proceed with troubleshooting.
Otherwise if size of the virtual machine decreased for instance from 20 GB to 2 GB - no data can be retrieved from this virtual hard drive as it has been erased after the crash.
In this case Support Engineer should inform customer that data had been erased and there is nothing we can do to retrieve it.
2) Next, you need to search for the exact error message and follow the troubleshooting guidance in related article.
3) If size of .hdd file remained the same, please try general troubleshooting steps to retrieve data, please follow this article:
http://kb.parallels.com/en/7096
4) If solution above does not help please follow troubleshooting steps in this article:
http://kb.parallels.com/en/112869
If none of the above solutions help, the virtual machine cannot be restored and client need to create completely new virtual machine in order to continue running Windows on his Mac.
