pagerank dilute

[Autoweb]

Hi,
I have a over a hundred text links on my home page to keyword optimised pages which have genuine content pulled from my database. The search pages were pulling many 1st page results on google, some were top.

I made a change by introducing these links onto another page...now after the pages have been cached I have taken an overall drop of about 5 positions for each page.

Have I in some way diluted my overall pagerank?
If so, can I disallow all the pages using a robot.txt file and then remove the "disallow" from the robot.txt file to allow them to be cached again?

I am a little wet behind the ears here...please help.

Thanks
Richard