spinning beach ball

imac, 10. 7.3

i just wanted to print something. but there came the beachball. i relaunched the finder, but that did not help. i could not click print and i could not click the apple to restart. so i did the keyboard control eject and got the dialog box and clicked restart. nothing. then getting desperate i clicked shut down, got dialog box, but no shutdown.
sometimes a program will cancel shutdown, sure, but it will tell me this. it just does not shut down.
never saw anything like this before.

anybody?

Have you eventually shut down by turning your iMac off at the mains?

If so unplug for a minute or two, plug back in, power up, boot and see what happens. If all is well go into Disk utility and run Verify Disk and Repair Permissions. Hopefully it may just be one of those glitches which seem to occur with software.