There are all sorts of drivers that do not cooperate with the power
schemes. On my computer, if I leave the HP printer on, the HP
computer will not standby or hibernate. Does exactly what you are
describing, comes back on in a minute (if standby) and refuses all
together if you are telling it to hibernate. With the hibernate, it
should tell you which program is causing the trouble. There is not
much that you can do about it, but you should be able to determine the
culprit by trial and error. Try powering down periphials before you
try to standby/hibernate and see if that works.