A0 suddenly acting as cathode on INPUT mode while Charlieplexing

I built and programmed a charliecube out of common anode LEDs, and it was working great. However, I noticed that certain lights were always on recently. I did some trouble shooting and found out that while set to INPUT mode, the wire connected to A0 is acting as a cathode for the other pins set to HIGH OUTPUT, causing some lights to turn on very dimly whether I want them to or not. If it is supposed to be on, it will then go up to it's intended brightness level. While I was trying to figure out what was wrong with it, I cleaned all the scraped off the extra contacts on my perfboard and wiped the whole thing down with alcohol just in case it was a connection issue, but no luck.

I had issues that were kind of similar with the serial ports being on digital pins 0 and 1 before, but I moved those connections to other pins which solved the problem. I'm thinking I may just change the pin for this one too, but I looked up the specs for a Nano, and the A0 pin doesn't seem to be any different from the next few analog pins, which are working fine. I have a feeling I may have damaged the board from toggling it's pinmode too quickly, but people have told me that's not possible.

I have a spire of the cube breadboarded at home that I left running for 5 days straight, and it developed the same issue on a different pin, which is why I think it may be some type of degradation

Schematic? Code (use code tags)? Pictures?

The only reason we could fancy for a progressive development of such a problem over time, is damage to the chip caused by failing to use current-limiting resistors.

Agreed, Paul__B. This is probably the same Charlieplexed RGB cube design we have seen several times before. That design has no series resistors and no transistors to handle the high currents.

I'm doing Asher Glick's design, which doesn't have series resistors. I knew it could be damaging to the circuit, but I thought it would cause a failure of the LEDs, not damage to the arduino if no series resistors were added.

Now you know better. Replace the chip and add current limit resistors.

As it is Nano, you can't easilly replace the chip (not without specialist equipment anyway). So you will have to replace the whole Nano. Fortunately they are pretty cheap!

The Arduino gets damaged worse than the leds, because its pins are forced to source or sink the current for several leds at once.

Series resistors that are high enough to protect the Arduino pins from that current may make the cube pretty dim. If so, you may need some transistors too.