You can try this, click the apple logo in the menu bar>system preferences>software update, installed software tab and see what has or has not installed.
Then click software update and write down the available updates for you mac. (name and version, Ex. 10.6.8 combo update V1.1)
Then set Safari preferences general to Save Downloaded Files to desktop.
Then go to this link and download the stand alone installer one at a time. Type the name and version into the search bar.
Download to desktop and then open the installer and run it. It is best to do this via ethernet rather than wireless as it is usually faster and less chance of RFI (radio frequency interference) that can cause corruptions.
If you have not installed the combo I used as the example start there then do the the others.