I recently experienced an issue where my vCenter Server Service failed to start upon reboot. After examination of the vpxd.log I noticed the vCenter service was being forced to shut down due to a port conflict. I looked through the Windows Server Services console and noticed that the IIS Admin Service and World Wide Web Publishing service was now present on my vCenter server; the two services were not there prior. I removed the services from my host using Server Manager, rebooted and the vCenter Server Service started normally.
I suspect a Windows Patch caused this to happen as my reason for rebooting in the first place was due to Windows patches being installed. I do not know which patch may have caused this specifically but for some odd reason unbeknownst to me the IIS service was suddenly installed and running on my server; thus, causing a port conflict with vCenter (and VirtualCenter Management Webservices).