I had my new computer case open on a table, ready for assembly, when someone leaned over it to look inside. I was wondering: if some dirt or food crumbs fell into the open case, would it cause problems later? It was just the case; I have not put in the motherboard or anything else yet.
It is a black case and I did not see any evidence of crumbs, otherwise I would have gotten some compressed air to blow it out.
No, nothing's that sensitive. Motherboards can get dusty and still function: http://4.bp.blogspot.com/_4YPTghPICMg/TO1583nq2jI/AAAAA...
Have you heard of breadboarding? People run their computers on open-air motherboards, and it works fine.
Liquid in the circuitry could be more of a problem, but crumbs will not be.
And the only reason dust causes a problem is heat buildup, clogging a heatsink full of dust will definitely kill a processor. Dirt or crumbs won't be conductive or capacitive to the point of damaging anything, so they won't cause a problem.