One side browns faster, cakes come out lopsided, or bases burn while tops stay pale. Most of this is not a fault, and a cheap thermometer settles which part is.
Common oven problems
All oven guides
Oven Baking Unevenly: Calibration, Racks and Bakeware
Oven Will Not Heat at All: Electric and Gas
An oven that stays cold while its display works points at the heating circuit, not the controls. Electric and gas models fail in different ways.