Most chassis are drilled and tapped for at least two mobo form-factors (like micro-ATX).
So, there are likely several more mounting holes in the chassis than any mobo could use.
Additionally, many case hardware kits include extra screws, either by mstake or on purpose ... and ... there are a number of other ways that the conductive brass standoffs can be "mis-applied" , usually one of the central holes is "mis-read" and then overlooked.
The gist off "all this" is that (surpisingly!) often, one of those brass spacing standoffs (that lift the mobo about 1/4" away from the chassis) can be "HIDING" in a place where no holes exist ... and, instead, that chunk of brass is creating a junction between two surface solder-points (or circuit traces) on the underside of the mobo. And, this condition can shunt power to ground, away from intended circuits.
FURTHER ... SOME people (lots, actually) never did understand WHAT the standoffs are for and do not install them at all ! ... THESE people screw the mobo DIRECTLY to the chassis without any standoffs AT ALL ! This shorts MOST of the silver solder points, on the bottom of the mobo ... definately a "NO GO" ... system won't make a peep.
... And ... Funny thing is, ... We "Veterans" can see how easily these mistakes can be made and all of "Techdom" is rife with such pitfalls, so we don't chuckle too much, 'cause it could be us "stranded out there", tomorrow.
The really good news is that, once these errors are corrected, most new builds "fire-up" just fine.
Any-hoo ... That covers the introduction for THAT point, on the TS Checklist.
= Al =