How can I access Time Machine files?

I installed an external 500 gigger external drive and dedicated it to Time Machine in June 2011. In October 2012 I upgraded to Snow Leopard and checked Time Machine only to find that all dates prior to that date were grayed out. I thus lost access to some important files since the automatic back-up began anew in November 2012.

The Finder indicates that the external drive contains over 100 GB of saved files which must be the ones under the grayed-out dates. There are no photos or movies on the Time Machine drive as I am using another external for those. I have used every trick and tried every advice given in this forum including a Utilities-Repair of that drive - to no avail.

How can I regain access to the contents hidden under the dates which do NOT light up when I pass the mouse over them?