Good to hear you are back up and running.
Most of the hardware in a computer is either screwed down or clamped down. But almost all device cards have only one anchor spot.. the backplane mount! A small thump or jolt can cause the card to loosen from its contact slot, and prevent the computer from powering on or showing life.
In almost all cases, it is a cause of the data bus being shunted. Normally, no harm done.
Memory is clamped down at the ends of modules, but still there is the remote chance they might loosen. The CPU is clamped down on its own, and the heat sink assembly is also clamped or screwed down. The older AGP type video card did have an anchor at its front end.. to prevent loosening from the socket. But not with the PCI_E versions. And with the video card having some weighty components, it can become displaced easily.
Power connections seldom come loose, but always good to check any item that connects to the motherboard or power leads.
F@H.. to solve mankind's maladies.. in our lifetimes!