Ok, here's the deal. One of my keys (I believe it's the C4 key) is acting strangly. When I press it softly, it either sounds like velocity is really low, or it's at 127! It's not constant, and I'm wondering if this is something that can be recalibrated or reset... any reply would help, including a number to call Korg for help. Thanks.

by the way, my keyboard is an N264...

Sounds like you have a key switch that's crapped out; otherwise the whole machine would be acting funky instead of just one key. If that's worn through or bent in some way, it could be "shorting out" where the processor's reading of its position is concerned. (That's not ELECTRICITY, just a faulty reading situation.) If so there could be a screwy default in place, resulting in a full on/off behavior.
First, go to Korg.com and ask for some tech help. THAT'll probably be a slow process, but you'll learn more and it'll work better being solved from the ground up.
Then find a local tech who works on Korgs. While you're at it, presuming you have the bucks, have them check the battery and ALL key contacts. That's a bit cheaper in the long run. Korg sells keys and a few other pieces separately as well, so if its just a leaf switch, a clip and 2 screws you need, it'll save your tech time and save YOU money if you go in with the proper information. And never spill a whole orange soda into a live PolyMoog. Don't ask me how I know.

I had the same problem in my X3. There is a rubber band along the whole keyboard with two conductive lines which 'touch' two contacts on a board for every key you press. Probably, the conductive covering is worn out or dirty.

I opened my X3, took all the screws from the one-sided PCB which has the contacts and I then could clean the conductive lines of the rubber with alcohol (if you rub too much I'm afraid you'll remove the covering). It worked OK for some time, but in the end I had to change it. I ordered a new rubber band from my Korg dealer and changed it (it costed about 5000 pesetas, $35 if I am right).

You could alternatively try to 'rotate' 180 degrees the band, and it could be that the worn-out zones do not fall under the key pressing points.

From what I've seen from the N364 & N264 their mechanics shouldn't differ a bit from the X2 & X3.

I hope it helps.