OS X :: Cannot Authenticate System Prefs Or Install After SL Installed

I am running a macbook only a couple of months old so i go the cheap as chips dvd for SL Installed it and things seem fine except the fun that office 2008 wont load at all (gotta love MS) Now though i can not authenticate myself to change accounts in preferences even though i am the only user and i am the admin user. i click on the lock and it simply saying "authenticating" then goes back to "click lock to change settings" this is annoying as i cant do much in terms of users etc and i think this is lnked to the fact that i can't install not programs. In fact i couldn't even install the additional programs from the install DVD!!! i got to the final button to actually instal after selecting the location etc and it does nothing after clicking install. No password prompt or nothing.