In the early days of hard disks this was a regular problem, due to the
spindle wearing...
If it is an old disk.. give it a sharp tap (nothing too heavy, maybe a large
coin?) just at the moment you apply power.  It must be on a solid bit... the
silver chassis is best. It used to work on early AT machines and before!!!
(I'm getting too old for this game).

If its an electronic problem.. leave it to the experts.. Vogon are not cheap
but V. Good.

Good Luck