Here we discuss everything related to riding, maintenance and gear.
Do you have any lights on the dash indicating it has any power at all? It's strange to suddenly lose all power, usually the bike will run poorly for a bit, or the lights/dash will dim, or the bike will still attempt to spin the starter with a battery issue.
If you have no power at all, I'd be checking the battery itself and the leads from it first. It's very strange for the battery to just die outright, so it's likely a lost terminal lead or something similar.
No lights at all on the dash. It seemed strange to me as well to loose power all at once. The bike was running fine right up until it died as well.
My initial thought is that a cable came loose or melted or I lost a fuse. I pulled the seat and side panels but couldn't see anything that looked physically wrong with any of the wiring. I tried reseating all fuses with no luck as well. I didn't have a multimeter with me on the trail so I wasn't able to do too much diagnoses.
I probably won't have time to look at it in depth until Sunday or Monday. I'll start by testing the battery and then probably start testing connections. I'll update the thread here with what I find.
I'd test connections first. Complete and total sudden shutdown with no evidence of electrical functionality at all indicates to me that possibly one of your battery terminal connectors came off, or one of the main battery cables snapped. I believe the KLX300 should also have a main fuse, coming straight off of the battery. Did you check that? On most bikes it is separate from the usual lights/horn/accessories/etc. fuses.
Update: I was able to find some time to test the battery with my voltmeter this afternoon. Voltage looks fine with the ignition off - but as soon as I turn the ignition on the voltage drops to near 0. So I believe the battery is dead.
I think the next question is if the battery is bad or the charging system. I'm going to throw the battery on a charger overnight and see if it will hold a charge. If the battery holds a charge I'll likely take the bike to the shop to get the stator, etc. checked out.
Almost any autoparts store will hook the battery up to a real load-tester so you'll know for sure. If you have a solid-state voltage regulator, they can fail instantly without warning. Ye Olde Fashioned mechanical ones usually show up: turn on high-beams, grab brakes, and you'll see the headlights dim. Did you test the battery cables? Were they tight and clean? (That seems like it should be a GoldMember quote.) Were the cable-ends tight? I had a positive simply slide right out of the factory-crimped end...