my friend your atv just went into the evil limp mode. you have 1 of 3 things that you can do. first is that there is a switch inside the clutch cover and i can't remember which way it is supposed to be set but it is incase your belt frey's it will trip this switch and it will go into limp mode. second and most likely is you had a power surge and you can go to your arctic cat dealer and get a reset plug which will reset the system and let you get out of limp mode. 3rd is you hit 100 hours on the machine and it will do that so it lets you know it is time to look over the machine. your best bet is this. DynaTek Black Rev box CDI Ignition 04-06 Arctic Cat 650: eBay Motors (item 280563082246 end time Oct-16-10 11:01:26 PDT)
this will take care of limp mode so it never happens again, it will make it so your machine runs cooler, you won't have to hit the ovveride button and most importantly it gives you a crap pile of power on bottom end. i would go with the cdi if i were you. if you do search around there should be a tutorial about resetting with the plug which is basically jumping two wires. edit: oh and while you are at it i would get a pink primary and black secondary clutch springs from EPI. then i would remove the larger shim of the two that hold down the primary clutch i believe. when you take the bolt out that holds the clutch in there are two washers just take the thicker of the two out. this will give you greater belt life and in my opinion a way funner power band with a harder backshift.