Roots-Will not hold color anymore

It sounds like you just aren't getting it all the way to blond.  Since you switched products and aren't highlighting, it sounds like you are just getting the brown hair to the orange stage, but not all the way to the yellow of blonde (which the highlighting may have helped you get to in the past).  Using the darker blonde will only make this worse because its lifting even less, equaling darker orange or light brown.  This is actually a common problem with boxed color, you don't know what base is in there, and it often comes out orange because not only does it not lift enough, it often has a violet base which does not counter orange that comes out if the hair you are starting with is dark blonde or darker.  You are probably going to need to bleach to get medium brown hair to blonde.  (You could try a blonde dye that has a lot of lift and a blue base, but your hair is dark enough that this even may not work.   If you went to Sally, that would be a high lift level 10 dye with a blue base, and 40 volume developer...but like I say, that may not work, you'd have to test strand it first and if you still get orange, try doing it twice, and if the test strand is too damaged or if its still orange, you will definitely need bleach to get to blonde).  I can't tell you what to get with boxed dyes, but if you want to use those, you can call the company and ask them which product has what you need in it, and if they make something with that much lift.