Um, if you problem is the same one that I have, you need to see if you have two different speed memory modules.
In my case, I had a 64MB 3-2-2 module and a 128MB 2-2-2 module. I pulled the 64MB module and my 450MHz DP G4 works like new.
(I didn't figure out this solution, I read about it somwhere in these forums...)
--Tom