Just found this, hope it helps someone :)
FYI: I'm running iTunes 10.5 on Windows 7 (64 bit), but apparently this works on Mac OS too......it may be due to upgrading o 10.5 last week, but I'm not certain that's what caused it. Anyway, on to the fix!
when you do anything in iTunes Store, itunes seems to hang showing "Accessing iTunes Store" in the banner.
- Open iTunes - go to the top bar, click the 'Store' drop down menu
- Then click 'De-authorise this Computer'
- Enter your password
- Close & relaunch iTunes
- Click 'Store' again then click 'Re-authorise this Computer
- Enter password
et voila, the store should work properly again!