MBP cannot shut down, log out or restart

My early 08 MBP has seemed to have lost the ability to do the above 3 functions. Pressing the power button does not bring up the shut down/restart/sleep menu and going through the menu bar and clicking "shut down" does nothing either. Pressing cmd + shift + Q does nothing when it used to bring up the log out option. It's only been like this the past few days, I noticed when I was prompted to reboot for the SMC update but OSX did nothing after I clicked the reboot button. The only way to shut down or reboot is to perform a forced shut down.

I've repaired disk permissions, repaired the disk, reset the SMC and the PRAM but nothing has worked.

Help please? Thanks.

 

I did try the shutdown and restart commands but when I typed "su" to start with it would not let me enter my password so the shutdown and restart commands did not work.

I had a spare hour so I ended up using time machine to restore my system to about a week ago. I've since performed the SMC update along with all others and it works fine. I'm still curious as to why this happened, if anybody has an answer I would appreciate it.