if you have the feature (map updates) included with the model you purchased, first you have to download and install Garmin Express on your computer, and then connect your GPS to the computer.
the computer should detect the GPS and synchronization instructions should appear.
Try turning it completely off, have a cup of coffee, turn it back on and put a fingertip at each corner of the screen at the same time. Should re-set it for you. If not, call Garmin. They are super helpful.
The battery lid contains the positive contacts. There are three little copper teeth grouped together. One of them needs to align with a single copper contact on the pod when the lid is back on and the little dot on the lid aligns with the little dot on the pod. This whole positive contact is stuck to the lid with adhesive and it must have turned out of alignment when I changed the battery. Gently pull it out, align as described, and stick it back in. Bingo.