Recently active topics in Google tagged with desktop

My Google Desktop Cache doesn't work anymore. I can still search for strings in the websites I visited. I just added a string to my website, I displayed it with the Firefox, then I did a google desktop search for the string. The page was listed as a result. I then tried to display the cached version of the site from the google desktop cache. The displayed page was empty but for the header "This is a Version of .... in your personal Cache ...". Also in the list of cached versions I don't get a preview picture of currently visited sites anymore. However, I still get a preview and cache for pages I visited before Feb 2nd 2008.

For some of the page I visited around that date I get the error message in the header:
"Dies ist ein Teil eines Indexabbilds, das eventuell nicht korrekt angezeigt wird."
(This is a part of a indexcopy, that might be displayed incorrectly.9

There are three pages I loaded between Feb 2nd, 0:52:36 (has a chached version) and Feb 2nd 0:57:07 (doesn't have a cached version). When I click on their cache history, I get the change to go to page 1 to 10 of that history, going to page 9 I can then go to page 1-18. Clicking any page higher than 9 I get an error page
"Sie haben versucht, auf die Versionen einer Datei oder Webseite zuzugreifen, die nicht mehr vorhanden sind."
(You tried to get a version of a file of website that isn't existing anymore)
Even though page number 10 should list versions from visits in March '08.

For other desktop searches I can go on pages further than 9. I also have previews for emails and *.txt files from my hdd even till as recently as now.

I used to use version 5.3 or version 5.5 or so. While trying to resolve the problem I installed Google Desktop 5.7.0805.16405-de-pb.

Is there a chance to revitalize my index or will I have to start a new index and loose all my website visits and all my instant messenger-interaction.
I don't know whether I can get cached versions of visited site, but at least I'd like cached versions of sites I'm going to visit from now on. Preferably without loosing my googel desktop history.

Thanks