3ds max 2010 viewport background disappears?

I just started modeling a 3d car in 3ds max 2010. To do so i used some blueprints of a car that i locked in every view port ( left view...front view..etc. ). The problem is that when i try to zoom-in one specific view port...my background image disappears ...when i zoom-out...everything is okay...it's like if the image does not fit the screen it does not want to show just a part of it ...i'm really confused..already tried all the background settings and nothing works . please help