I have a nano powered by a 9v supply to the Vin and Gnd pins. A simple 'blink/fade' program controls a small string of LED christmas tree bulbs (I have a 3' tree in my backyard I decorate). Everything was working fine for a few days then the lights started going nuts. The routine would lock-up keeping the lights on or blinking, then it would jump to the next portion of code and lock-up again. If I unplug it and wait a few minutes it will run fine for sometimes 5 minutes, sometimes 5 hours but it keeps doing it. I had bench tested it just using USB power and it worked flawlessly for days straight while I tweaked the lighting effects. Lights are connected to GND and D9 for the PWM output to fade - they are 5v LED.
Measure the voltage at that 9 volt battory when the circuit starts to fail!
Post a drawing and data sheets for the LEDs.
I get 8.96v when it 'dies', there are no drawings or datasheets for the LEDs, they are tiny little battery powered (4.5v) lights that I cut and power via PWM (they are dimmable).
Solved: Defective/dead board. Connect through USB power to upload a simple program and it freezes - won't upload or do anything at that point. Dead Nano. 
Did you power the lights from an output pin?
How much current do they draw.
A pin can only safely provide ~20mA.
Anything more, and you have to use a transistor.
Leo..
ericmlaing:
Solved: Defective/dead board. Connect through USB power to upload a simple program and it freezes - won't upload or do anything at that point. Dead Nano.
Disconnect every external device, download a tiny test sketch that uses Serial Monitor via Serial.println("I am alive");
Forget that 9 volt battory! It is a voltage source and not a power source. Use 5 volt, via USB charger or similiar.
Note the current limit of 500 mA for USB.
It's a 9v POWER SUPPLY not a battery, I never said it was. I have NOTHING connected to it and when plugged in to USB, as stated, it just freezes... won't upload, won't do anything. To Wawa, I'm pretty sure they are REALLY close to 20mA and may have fried something - hence, dead Nano (but from what I did, not a Nano's fault).
How do You practically connect that 9 volt supply to the USB connector? USB must bring 5 volt, nothing else, absolutely nothing more..
Per my first post "I have a nano powered by a 9v supply to the Vin and Gnd pins." I know you have like WAY more posts and are probably way smarter than me at this stuff, but please, read.
ericmlaing:
Per my first post "I have a nano powered by a 9v supply to the Vin and Gnd pins." I know you have like WAY more posts and are probably way smarter than me at this stuff, but please, read.
Can be frustrating sometimes can't it. 
In Your reply #7 You are involving USB....
My mistake about the 9 volt.... 9 out if 10 members using 9 volt to Vin use that poor fire alarm battory. Usual pwr supplies used are 12 volt. 9 volt real supply is rather unusual..
In any case, the "Vin" pin is essentially useless.
Not only does the Nano require 5 V to operate, but you are attempting to power other things from the Nano outputs.
This is not workable - because the regulator on the Nano board has no heatsink to speak of. Draw more than one or two hundred milliamps and it will overheat and shut down - usually reversibly.
You need a 5 V supply for any serious project.
Mind you, your unseen code may also be the problem. 
first, a clear schematic would be in order. hand draw or computer draw and label things.
The question is about power moving through the board and the circuits.
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on the nano, do you have power and the unit working, just not able to upload ? or is the thing bricked ?
being impatient, I connected a thing wrong and blew the protection diode on my Nano, with all the 'how to fix' sites, seems I am not alone. had to replace the diode on the bottom of the board.
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since all things electronic run on smoke, there has been a need for some way to fix things.
Sparkfun used sell, but discontinued sales of the Magic Smoke Refil Kit
I did some research to see if I could replicate it. The crystalline structure of the silicon that makes up the chips seem to crystallize in a tetrahedron form. The Angular lattice of the silicone vaporizes, but the structure remains partially intact, vaporization emits what we call magic-smoke.
By a rather complicated osmosis process, it might be able to be replenished. The best I could figure is that it would be a process of :
Tetra-Osmosis Tetrahedron Angular Lattice Binary Sedimentation
The acronym does not sound quite as scientific.
Paul__B:
You need a 5 V supply for any serious project.Mind you, your unseen code may also be the problem.
I'll swap to a 5v supply but even when just using a USB connection to my computer nothing will upload.
My code is literally the FADE example but I have it go both ways - fade in fade out.