After trying multiple times, a coworker is not able to fit a motherboard in a computer case, and is having difficulty aligning screw holes in the motherboard to standoffs on the bottom of the case. which is most likely the source of the problem?

The most likely source of the problem is the form factors of both the case and the motherboard. They do not match. The type of motherboard describes its general shape and the kind of case it can use. For instance, you cannot have a full ATX motherboard fit inside a baby AT case. These two variants differ in width and will most likely cause overlap while installing. Sometimes, some system cases are not drilled to support all the mounting holes on various motherboard factors. This also causes significant issues while installing