Is it possible it's partway through one of the big W10 updates?
In which case leave it of for an hour or two.
If definitely not booting at all a common issue is memory not seated well enough.
If you're happy to open it pull the RAM memory out one at a time and reseat.
If that doesn't work leave one out as it will still boot on the other(s) but a faulty card will stop it dead.