Monitor no longer sleeping after 10.8.2 & Mac Mini EFI update

Question

Hopefully someone can help out here, my new 2012 Mac Mini was running fine without any problems, then when I installed the 10.8.2 update (not the original update that got pulled from the Apple site but the newer version) with the EFI Mac Mini firmware update my monitor won't go to sleep anymore. It used to do this without any problems, but since the update it goes to the screensaver without any problems but when the time comes for the monitor to go into sleep mode the screensaver just stays frozen on the screen until the Mini itself goes to sleep. Anyone else had this problem and managed to solve it? Thanks!

Answer 1

OK, as a further step, I typed pmset -g assertions into Terminal and got this response:
11/04/2013 00:09:15 BST 
Assertion status system-wide:
  PreventUserIdleDisplaySleep    0
  PreventSystemSleep            0
  PreventUserIdleSystemSleep    1
  ExternalMedia                  0
  UserIsActive                  0
  ApplePushServiceTask          0
  BackgroundTask                1
Listed by owning process:
  pid 4975(storeagent): [0x0000000c00000811] 134:51:07 BackgroundTask named: "com.apple.storeagent.UpdateStaging"
  pid 164(coreaudiod): [0x0000000100001adf] 01:18:15 NoIdleSleepAssertion named: "com.apple.audio.'AppleHDAEngineOutput:1B,0,1,2:0'.noidlesleep"
Kernel Assertions: 0x0132
* Kernel Assertion ID = 500
  Created At = 01/01/1970 01:03:17 GMT+
  Modified At = 10/04/2013 18:42:18 BST 
  Owner ID = 0xffffff80914ab000
  Level = 255
  Assertions Set = None (4)
* Kernel Assertion ID = 501
  Created At = 01/01/1970 01:03:24 GMT+
  Modified At = 05/04/2013 00:51:26 BST 
  Owner ID = 0xffffff8032426000
  Level = 0
  Assertions Set = None (4)
* Kernel Assertion ID = 502
  Created At = 01/01/1970 01:03:25 GMT+
  Modified At = 07/04/2013 23:05:42 BST 
  Owner ID = 0xffffff803244c000
  Level = 0
  Assertions Set = None (4)
* Kernel Assertion ID = 503
  Created At = 01/01/1970 01:03:31 GMT+
  Modified At = 10/04/2013 18:27:29 BST 
  Owner ID = 0xffffff8032403400
  Level = 0
  Assertions Set = None (32)
* Kernel Assertion ID = 929
  Created At = 11/04/2013 00:11:02 BST 
  Modified At = 01/01/1970 01:00:00 GMT+
  Owner ID = 0xffffff8032561900
  Level = 255
  Assertions Set = None (128)
anyone got any ideas what these processes might be and how to stop them?