Well, yes you should have just one. I have the Denon 988 and W7. The rest is guess because I have never seen that in over 5 systems. What we don't know is how stock is your OS and what combo of buggy drivers you may be using judging from a flood of no response?
Hopefully someone has seen this and will respond shortly. Me, I would search for like problems on internet incase Denon has a firmware bug in your range of models, but very unlikely. Uninstall ALL my AV software to rule out any DLLs or other conflicts. If problem still there then I would suspect something has been corrupted or broken in W7. In that case a restore or clean install should put you straight. All of the above can be painful.