What is one common reason for a PC not to power on after a hardware change?

When a PC does not power on after a hardware change, one common reason is an unconnected power button. This can happen if the case front panel connector for the power button is accidentally disconnected or not properly connected to the motherboard during the installation or upgrade process. The power button is a crucial component that signals the motherboard to start the boot process. If this connection is not secured, pressing the power button will not send the necessary signal to turn on the system, leading to the appearance of a non-functioning PC.

In contrast, while incompatible RAM or a faulty power supply can indeed prevent a PC from booting, they are typically associated with different symptoms or issues. An outdated BIOS version might affect compatibility with certain hardware, but it usually does not cause the system to fail to power on at all. The situation of an unconnected power button directly relates to the immediate action required to initiate the power-up sequence.