In Application Manager:
Disable and save each repository (will be greyed out when you do this) then allow it to update the catalogues. After catalogues updated, go back in renable and save each repository and allow it update the catalogues again.

Otherwise, as Radicalz38 mentions, may be a problem on your end if you can't access the repos.

Just wondering, do you have the same problem through fast app manager? Or if you do a manual "apt-get install" or "aptitude install" in xterm.