My 2006 Grand cherokee is completely dead all of the sudden. It was fine this morning. I went into the garage and it is completely dead. No dash lights, can't unlock/locl the doors with the key etc. It is as if the battery is totally dead. The battery may be dead, but I find it hard to belive it happened this quickly. Nothing was left on or anything.

Sounds more like a bad connection at the battery. Remove the terminals and clean them and then see what you have. If it starts, good. If not you want to check the battery voltage using a meter, then re-charge, test the battery, then the charging system. If everything is ok, test the system for draw.(something staying on, even if you did not turn it on) You need an ammeter to do that.
There are fuses you should also test inside the power distribution center near the battery also.
If you need more help on a specific item, just ask.