Why do I have no power to my motorcycle?

I have a 1980 Honda Cm400T it passed inspection a few weeks ago and I rode it two times after that. Then I parked it in my garage because it was getting colder outside, few more days later I tried starting it up again but once I turned the key in the ignition no power nothing at all, no lights, nothing. I renewed all the fuses, even charged the battery since it only had 12.03 volts. I don't know what else to check and why there's no power at all.

I would also make sure both ends of the battery terminals were attached and clean up both ends until shiney first. Good info on this thread about other potential issues.
http://www.hondatwins.net/forums/64-electrical-discussion/40748-1980-cm400-no-power.html

Start switch and kill switch (if equipped) are likely corroded or start relay is bad. Get a test light or DVOM and start troubleshooting. Check first if the starter is getting any power (when cranking) and check for a good ground.

Clean all the terminal in the heavy gauge wiring. (Most likely problem at the battery ends but don't forget the earth cable to the chassis/engine.

Have the battery load-tested at a shop that handles motorcycles. The battery can show 12+V but the amperage may be very low due to a dead cell or two.

On a bike that old my bet is that a earth/ground to the frame has been corroded and the cold weather (where metal will contract) has shifted one of the connections sufficiently to break the circuit. So it is a case of checking all those connections, cleaning them up with some emery paper and making sure you have bare metal connecting to bare metal.

A continuity tester can help you find the problem.

Start with -, negative battery post and cable, trace back to frame, switch and make sure the connections are clean, snug and cable/wire is complete. Still no current? Then time to trace positive cable/wire set. Ignition switchs can get corroded inside- use jumper wires to bypass switch and if lights work, try jumping starter- that would indicate ignition switch failur or wire ends to ignition switch. Starter relay is another point to check- right side just in front of battery, look for small wires that plugin from ignition switch- might need to take of fuel tank to get close look at wires around neck area- a known place for rubbing and shorts. Taillight wires just under rear of back fender can be rubbed by tire at times when overloaded, brake switch can be stuck also and that can lead to slow drawdown. Cable ends with insulation may look good- but peel back the covering a short distance and ou may find corrosion, broken wires. Test lights are very handy, VOM better for checking resistance but test lamp will show if wire broken, help to find poor grounds.

Good advice is check the battery terminals. When there's a high charge, like way above 15 Volts on any of the refs, the acid inside may have boiled out (this acid or white powder is potentially dangerous. When charged the battery has to be 12,8 Volt. When down to 12,4 I don't see any headlight functioning anymore and 12,2 Volt is virtually empty. An older battery will have to be replaced when the weather gets cold, good you mentioned you charged it manually but now check if it received more then a surface charge like when the lights go out after seconds. Surface charge isn't good enough for the starter.

The ground (- terminal) to the frame will be corroded underneath in case it is. Loosen this connection, it will be where the frame meets the engine.

Some engines require the emergency Stop switch in the On position. Others would only unable the ignition.

Check fuses. The connector to the Regulator.