I think the most likely scenario is that something got moved out of place (a connector or card or plug etc).
I would power it down and unplug it and go through the connections one by one. I would disconnect them, inspect them for anything odd or any debris and reconnect them.
You don't have to do all of them at once. You can do some and then try it....and then do some more....and maybe save the CPU for last as it is usually the biggest pain.