You are welcome.
As for the "why"....
Over time as computers heat up and cool down the components and connectors tend to expand and contract.
As a result they slowly creep loose and can settle on the threshold of being functional for some amount of time.
Then some touch, bump, movement (or dusting) completes the movement and connectivity is lost. It only takes one misconnection out of many to cause the problem.
And it always seems that, indeed, nothing specific happened or was changed.
Overall, there is a lot to be said for cleaning, dusting, and reseating the components on regular basis but without over doing it all.
Likewise, doing the same is often a good starting point with respect to troubleshooting.