[porrid]

Upon Restarting and after downloading and installing the latest Security update for Snow Leopard my 2008 iMac got stuck on the blue screen. I then lightly touched the start button putting it to sleep, but almost immediately after that I woke it up by touching the keyboard, and the Log-in window appeared.

I logged in installed a couple of new apps then chose to do a Restart and exactly the same thing happened. But upon repeating my last solution it remained in the blue screen. So I shut it down turned my modem off.

Although it fired as per normal after a while I decided to do a Restart to see if anything had changed - but no it hadn't !

I'm hoping this is not just my machine ?

[P]

Sounds odd. What happens if you unplug everything except the mouse and keyboard before rebooting?

[porrid]

I don;t now, didn't think of that one, I'll try that next time I reboot thank you.

[sammytt]

After updating to 10.6.8, same issue. Upon restart, hung up on blue screen. Also, when restarting again, hung up on logging out of main user account.
iMac Intel

[P]

Try booting in safe mode. You access safe mode by pressing shift directly after you hear the startup tone and releasing it when the booting is finished.