When a camera shows no sign of life at power-up, the unit itself is often not the culprit. Working through the following order usually pins the problem down within minutes.

1. Verify the supply first: measure the actual output of the adapter with a multimeter and compare it with the nameplate rating (commonly 12V/2A). With PoE, confirm the switch port has PoE enabled and that the port can deliver the power the device needs.
2. Then check the cabling: thin or over-long power leads cause voltage drop; for 12V runs beyond 30 metres, take power locally instead. PoE runs must use oxygen-free copper cable, as copper-clad aluminium drops noticeably over distance.
3. Read the LED: a healthy camera shows a steady red or blinking green indicator. Nothing at all points to the power path; a lit LED with no discoverable device points to the network.
4. Bench-test the unit: bring the camera indoors and connect it to a switch with the original adapter and a short patch lead. This cleanly separates a failed device from faulty site wiring.

If it still will not start on the bench, contact your supplier about warranty. Do not open the housing yourself, as that compromises the seal and the warranty.