1992 Yamaha FZR 600 TURNS OVER NO IGNITION!?

i have a 1992 Yamaha FZR 600, i bought a new battery and it just cranks and never wants to start. i checked the spark plugs they are a little dirty but look fine. i tested to see if they sparked but there was no spark.. could it be the CDI box? the digital ignitor? or a carb problem? any advice!??