System not shutting down when entering sleep

[fw2010]

Hi;
Windows 7 Ultimate X64 SP1 system.
All has been fine until I installed Firefox 29.0 upgrade (with Mozilla Maintenance). Now, when I put the computer into sleep mode, the screen blanks (monitor goes into power save mode), but system keeps running. When I press power button to resume, Windows logon screen appears, and all is OK when I am logged in.

Now the details:
This problem only occurs after I have waited about 1min or more from boot (cold or warm). If i go into sleep before that time, the system shuts down normally.
This being the case, I opened Services and checked for anything that has delayed start. I found two items.
It turns out that the [FONT=&quot]PnP-X IP Bus Enumerator service is the problem. When it is enabled (automatic - delayed start), the problem occurs. If I stop the service, then wait about 30 seconds for all of its processes to shut down, sleep mode works properly. If I start it again and wait 30 seconds for processes to start up again, sleep mode does not work properly.

I have temporarily disabled the PnP-X IP Bus Enumerator service. It does not appear that my system needs to run it. I have not found anything that doesn't work as a result.
That said, I would rather solve this issue properly. The PnP-X IP Bus Enumerator service was not causing any issues prior to upgrading Firefox. Perhaps there is another program causing the problem, but I do not recall installations other than the Firefox upgrade since the last time sleep was working properly. I have not yet tried uninstalling Firefox, but I think I should try that.

Any ideas?
Thanks

FW
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[DavidE]

The default startup type for the PnP-X IP Bus Enumerator service is Manual, so something changed it on your system.
Maybe a Media Center device, XBOX, ... ?

I found this old thread where someone reported the same issue, but there is no reply/solution
http://www.sevenforums.com/general-discussion/243911-pnp-x-ip-bus-enumerator-service-tweaks.html