OS X update in App Store

Updated iMac (early 2009, 24-inch, 2.66 GHZ Intel Core 2 Duo, 8 GB 1067 MHz DDR3 Memory) to OS X El Capitan. App Store shows OS X Software Update available but can't update. Progress bar shows installing - calculating but nothing is happening. The update buttons are grayed out and can't click on them.

2nd part of this problem is with iTunes update. As part of this OS X Update it shows iTunes 12.8.2 and shows the same progress bar which shows installing, but nothing is happening; same as mentioned above.

Further down in the App Update list under Updates installed in the last 30 days it shows iTunes 12.8.2 was installed today, April 18 but when I check About iTunes it shows v.12.8.1.3