An aluminum electrolytic capacitor that has overheated or degraded, causing the electrolyte to vaporize and expand. The pressure pushes up against the scored metal top of the can, creating a visible dome shape. Finding one on a printed circuit board is an immediate indicator of a failed or failing power supply circuit.
The monitor won't power on because there's a massive bulger right next to the heat sink on the power board.
Always replace a bulger immediately, even if the circuit still sort of works; it is a ticking time bomb that will eventually leak conductive fluid or pop.
Related terms
Electrolytic capacitor
A polarized capacitor that uses a chemical electrolyte to achieve high capacitance.
Capacitor plague
A widespread issue in older electronics where poor-quality electrolytic capacitors bulged, leaked, and failed prematurely.
ESR
Equivalent series resistance is the internal resistance that appears in series with an ideal capacitor or inductor.