Take the CDI off, smack it back side down on the workbench or floor hard a few times and try it again.. Just to rule it out! LOL... I only suggest it because its worked for me a few times. Then you know its time to get a new CDI on there.
Other than that, as already suggested go through every connection, every part, kill switch is a good one that can be causing problems. When you had it running how did you shut it off? If you used the kill switch or ignition switch they may have issues. You can quickly unplug them to rule them out as shorting the ignition kill wire.
Fresh plug and freshen up the ends of the plug wire. I know that gets said over and over on here but its just one of those common quick fixes that can give good results sometimes.
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1984 Honda ATC200ES "Big Red"
1982 ATC200E "Hondie"
1988 TRX300FW "Project Quad" Still in progress....