ubun2

I'm running ubuntu 9.10 Karmic Koala
I had originally messed something up by accidentally changing permissions on /usr/bin to 777, which disabled me from using sudo.
fixing the permissions by root shell, and now when i try and start up my laptop it gets to the
 
"
Ubuntu
<progress bar thing here>
"
 
and then flashes between that screen and a black screen which says "*nmpd is running" or something.
 
Do i have to completely reinstall ubuntu or is there a way i can save myself? Please help!