Guys,
I installed Win 8 Preview on my two PCs and laptop months ago. Recently, all of them started having shutting down problem. when shutting down there were notice that windows isn't properly shut down, need to restart, then restarted. Sometimes it just restarted when shut down without any notice. It is now getting tricky to shut down, I did some step like disconnecting the internet, terminating all working program (usually I don't). It works once, but not at the next. Is it due to some updates, or something else?
Please share if you have the same problem.

Thanks Pooch for the reply I check the msconfig but afraid of wrongly picking or unchecking
I did suspect there is something on the background stalling the process. But dont know whether recently installed program or installed updates. I feel like suspecting the updates as that were the only same thing done on all three of my PCs and NB.
I'm pretty sure about it because those three rigs have different installed program according to its function.
My PC at the office only has Office 2010, ACDSee, Photoshop, Vuse, and some small utilities programs.
My NB also has minimal programs installed, as I only need it to run my presentation or teaching activities.
My home PC has a bit extensive because it has some games like PES 2012, MotoGP, NFS Hot Pursuit, and some more.

I planned to look over the updates and also the most similar programs installed on three PC.
Not thinking about viruses yet

Yeah Pooch...
I agree, considering updates make better. But could also be a case that the update interfering with certain program that becoming uncompatible with it..? As you suggest the AV program mostly don't do well with Win 8, so I stick with MSE and always have it updated. I already started with my Laptop by disconnecting it from the wireless modem before shutting it down. It worked once, but later the "Your PC run into a problem that windows can not handle. Need to restart" notification appeared (something like that). All driver are up to date so far (I work with 64-bit system). I found out that the driver of wireless modem was the only little bit incompat with the system (tricked it through the connection manajer, and left behind the native program from the modem), but it works. I reserve the system recovery as my last option on home PC as My son has some of his saved game to be backed up or he will throw a big yell at me
OK then. I will continue sorting out the matter, and give you some head ups.

Cheers...!

i've noticed, that usually when i try to shut down my computer it will:

1) shut down as it should (about 10% chance)

2) show the 'shutting down' screen and returns back to the desktop (programs closed) and then when you shut it down again, it will do as 1) (75% chance)

3) shut down (either way as above) and turn off the displays, and stay on until the computer times it out.