Why is the sync button shaded/ grayed out in iTunes when I try to sync my iPhone 4s

10-11  Source: Network gathering  Views:2 

I have 2 iPhone 4s', I originally synced one last year to the same computer I am using now, it worked fine. I have all the latest updates for iTunes and IOS. I am using a windows 7 laptop.
When I try to sync my phone, iTunes takes a very long time to find my iphone after I connect it and sometimes freezes for a minute or so. I then do all the regular things such as ticking the sync only selected songs, sync with this device over Wifi etc. but then when I have selected the songs i want and click 'apply', iTunes freezes again for a moment and the sync button at the bottom remains shaded out so I can't click it??
I have ticked automatically sync this device when connected, uninstalled/ re-installed iTunes 4 or 5 times, restarted my computer, authorised my computer (again), backed up and reset my iphone. Re-installed Bonjour, reset my Wifi router as it also does not let me click the 'sync now' button on either of my phones and after all of this, none of the songs in my music library on my iphones have changed??
Can anyone please help?
Click here and follow the instructions.
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