Having trouble deactivating my demo giude on Garmin c330

Any chance that you could have purchased a store demo unit? My Nuvi never had a demo on it and yours is the first post I've read that talks about it. Oops -- after typing the previous sentence, I decided to search for "C330 Demo" and I found:
http://www.poi-factory.com/node/7348

I did a brief Google search for your problem and found a couple of different posts about it. They don't exactly agree with each other so I'll paste them both here and you can read them and.......

One thing you may not be aware of is that there should be a "reset" button under the front bezel of your unit. It's detailed on page 28 of the manual located here: http://www8.garmin.com/manuals/StreetPilotc330_OwnersManual....

Here are the relevant posts I found:

POST #1
demo mode in the devices can be 2 kinds:
1. If user entered DEMO unlock code and transferred maps to the device. It can be cured by flashing another maps without demo code (delete code in Mapsource).
2. Demo unit made by garmin. Ususally these units are refurbished old broken units, with water on motherboards, strange gps-chip behaviour. So, garmin turns off gps-chip, flashes demo-version of the firmware, and put this unit to the stocks for DEMO purposes, assuming that these units really for demo.
But sellers may be want to sell everything... So, sometimes devices appeared on ebay.
This demo device is capable to revert to normal state only with soldering iron (usually), and long firmware replacement (not trivial for usual users, so it's impossible). It useful also for parts to recover some broken units (display, keyboard, buttons, etc..), nothing else.

POST #2
Here is how to deal with "DEMO" modus.

How to enter it.
1. Get hold of any map you like to test on your GPS (any Garmin)
2. It will tell you that the map is locked after you have installed in your PC.
To unlock add "DEMO" with out quotes where you normaly add 25 digit code.
This gets MapSource into demo modus, and unlock all map (and all region)on your PC
3. Transfere some mapsegment to our GPS.
This gets your GPS into DEMO modus.
In this modus the GPS does simualte the signals, and all maps are unlocked.

To get out of "DEMO" modus.
1. In MapSource view your installed keys, and delete the "DEMO" key.
2. Transfere some free maps, or locked maps that you have key for, to your GPS
This removes the maps with "DEMO" tags, and your GPS should work ok.

You could always just call Garmin: 1-800-800-1020

It's a free call and their phone support is excellent.