She just won't start anymore

So I have a 1978 XS650 Special. I just got the bike completed, fresh paint, new tires, she is ready to ride. I started it up and ran great on the lift. Shut it down, did some little working on the bike and started it again (same day, within 1 hour apart .. both kick and electric start). Later in the day, I went to show my wife how to start her (since it is her bike) and the bike won't start. The starter chugs, but nothing. I took the plugs out, cleaned them up and tried again ... nothing. So then I took the plugs out and I have no spark on either side. Check the fuses, all is good. Now when I bought the bike, the previous owner had bypassed the start button on the bars and put a start button directly off the voltage regulator. When he was starting the bike, he had to hit his relocated button and turn the key on at the same time to start the bike. I thought maybe he had a bad ground ..... SO with all that said, could there be a bad voltage regulator or a bad start switch that's just allowing power to the starter, but no spark to the plugs? Why would it work one moment and not the other? Thanks for any help!

Maybe you've run the battery down. The ignition needs battery power to function, at least until the engine starts and the charging system kicks in. If the battery gets low, it may have enough juice to spin the starter but that won't leave any to power the ignition. The bike will crank over but not start. Try kick starting it, that doesn't draw any battery power so what little you have should go to the ignition.

I have a full battery. At first I thought that may be the issue too, so I made sure to charge completely. When I first started it and it ran, I started it with the electric start and the kick start with no problems. Then when it stopped starting, I tried both ways too and got nothing

Well then, if you're sure it's a no spark issue, it would be time to start checking the ignition system and it's components. Do you still have the stock points ignition?

Yeah, still have stock points ignition. So you don't think the start button/run off switch would be bad?

The starter circuit isn't connected or related to the ignition circuit. If there's something wrong with it, that shouldn't effect the spark.

Are the points old or new? Old ones can have the spring get weak so they don't close up properly. If they don't close, the coil won't charge up for the next spark. That means no next spark.

With the ignition switch on and the on/off switch on check you are getting voltage at the coils, if not the problem the problem is between battery and coils via the switches, if you have voltage it will be between points and coils.