Since it's a guest issue you will have to troubleshoot the issue. I would go into Linux recovery (with Linux CD) and look at the boot logs for any issues. Normally when we have a unclean start up it's a file system that needs a fsck. It can also be a driver or network nic no longer configured correctly... I bet my money on the fsck but the logs should help you diagnose.
Let me know if you have any questions.