Oh God Help audio/midi setup and apps on mac wont open

man something really not good is happeneing. I cant get any 
midi deice to work and the audio/midi setup says if a 
installed a new driver to get rid of it and try again 
(basically) and the bad thing is now no programs will open 
either. I have a mac G5 always stable the two most recent 
things I put on here is a n rme 400 wwhich was fine. I also 
have among other thing tascam `884 , I did something today . 
I was using the rme 400 lightpiping the 1884 inouts and when 
I sdisconnected  it now I cant open and well I said the 
problem up there. 
With out getting too deep in the things I did today on my 
system , maybe someone can give some advice on how to get 
back up