My Tahoe has no power and the battery is charged and alt is good. Before I had no power there was a clicking sound under dash. What could be the problem?
Check all of the fuses first in the under hood fuses panel and under the dash.
Make sure all of your battery connections are clean with no corrosion build up on battery cables at both ends.
Check the fusible link on the positive cable; it's the thinner wire on the positive cable. Make sure there is current on both sides of the molded plastic block on the wire. If the fusible link is blown then repair the link as needed.
Let me know how you make out with these suggestions. If you need more help then we can diagnosis the problem further.