What causes the electrical system to stop working on 2003 Volkswagen Passat W8

Everything electrical stopped working on my daughters W8. Windows, powere locks, etc. What causes this and is it going to be an expensive fix?

Asked by for the 2003 Volkswagen Passat W8
Always start with the basics and check all battery connections. On this vehicle there are typically several fuselinks at battery or somewhere down the cables.