I have seen a few times that a guest VM can get stuck in long boot up periods. This can happen when you deploy a normal server from template, or if you create a new one. What I have noticed is that the problem doesn’t happen until you give the server over 4 gigs of RAM. The server can act normal, but will take unusual long time to restart. The problem happens when it gets to the Windows splash screen, and the bar keeps scrolling. This can literally take over 10 minutes to restart.
I’ve seen this in server 2008 and 2003. It is a pretty common bug that I heard was going to be fixed in vSphere but wasn’t. To resolve this issue I edited the settings of the problem VM and lower the RAM. In my case I moved it back to it’s original size that it had in template. Turn on the guest and make sure it boots correctly this time. If it does, then you are fine to add the memory back to the much larger size without having the same issues. I believe this problem mostly occurs when you adjust the memory and other things right after a deployment.