Ah-HA! Well, I pass on the unlocking stuff, but at least you have Mapsource so everything else should be straightforward.
Check:
Did you install Trip & Waypoint Manager first?
And the USB driver (part of the same install)?
Then added Mapsource? (Which effectively becomes an 'upgrade' to T&W Man, very similar interface.)
I've always found Garmin's software installs routines very flakey BTW - easy to exit too early.
If you power the Garmin before connecting, do you get the 'chime' or some such indication as soon as you connect to PC?
Now, in Mapsource and 'Transfer', and 'Send to Device' - after a short pause your GPS should be ID'd including the model type and a serial number - shown on screen. And up to 4 tickboxes below allowing you to select all or none of Maps, Tracks, Waypoints and Routes.
A successful transfer will end with a 'transfer successful' or some such message on the PC.
Sometimes there is also a message on the Garmin screen. A bad transfer (usually duplicate or too many waypoints) sometimes pops up failure messages on either PC or Garmin - always check both before disconnecting.
[edit] unlocking - in Mapsource - Utilities, Unlock Maps
[and edit] since you have Mapsource, you should never need to see the GPS as an external drive (at least, not until you need to retrieve recorded tracks off the card - which is not enabled by default BTW)