Brown hair or blonde hair?!!!

[Guest]

I have naturally dark blonde hair but have been dying it dark brown for the last year and a half - the other day I had it highlighted at the hairdresser's as I was getting blonde roots through - the result - light blonde roots, no highlights visible anywhere else in my hair except the roots!!! How can I get the rest of my hair lighter and so I don't look as stupid as I do now? My hairdresser says the build up of dye in my hair is why the highlights haven't absorbed everywhere!!!

Help! Please!