System hangs after power on reboot

I am running Lion on a 2011 27 inch iMac. After waking it up from sleeping, the screen displayed and I selected the Mail app but it did not activate. I selected Safari but it would not activate either, so I tried to select the Apple icon to try an force quit any application that might be not responding but it wouldn't select. With nothing responding ( mouse clicks, Control-C, Esc ) I powered it down. I even unpluged it from the power to do a SMC clear, and when I powered it on again it booted, and all the applications that were started before, (Mail, Calendar, Terminal, LibreOffice, Photoshop, and Chrome) all displayed a window, BUT, the system did not respond to any input (mouse clicks, Esc any Control key sequence). It was just unresponsive. I have tried powering it down and rebooting several times but get the same results--- APPs seem to start but the system appears to be hung.
Any suggestions?

Reboot to the Recovery Partition (hold down command + r) and run Disk Utility from Utilities. Do a Verify and Repair on the hard drive. The symptoms you wrote about could be related to a failing hard drive. Let us know.

You should also know that Apple has recalled all Seagate 1 TB hard drives in your model iMac because of a defect. Were you notified about it from Apple?

The Verify said everything looked correct, the Repair naturally didn't do anything except say things were okay. After restarting from the Recovery Partition things were operating normally.
Thank You very much for your reply. I don't know what it did but it now works again.

And BTW, Apple did not send me any notice that there might be problems with the Seagate drive.

You might wish to give Apple a call and have the SN of your iMac on hand when you do. The 2010, 2011, 27" and 21.5" iMacs that have the Seagate 1 TB drive installed have been recalled. Apple will replace the drive for free even if the machine is no longer in warranty.