Used bike = carb problems. I'd pull them apart and do a thorough cleaning. Here's a little procedure I wrote on how to do it:
Pull the tank, remove your choke cable, drain your float bowls, loosen the screws on the carb boots, remove entire carb bank and flip it upside down. Pull float bowls, remove your pilot and main jets and clean them with carb cleaner. I'd also squirt a bit of carb cleaner into the fuel inlet ports and also clean the little rubber stoppers. No reason to pull the throttle cables and make sure you put an old rag over the intake ports so you don't lose any screws in unwanted places. After cleaning your pilot jets, it's a good idea to blow compressed air through them to make sure they're open.
I'd also check the float bowl gaskets for cracks. The are 15 years old after all!
As far as no cranking, could be several things...Kickstand switch, clutch switch, starting circuit cut off relay, starter motor, main switch(key), start button. A couple of questions, have you tried it in neutral? Does the neutral light work? Do the lights work? Do you get a spark?
Mark