|Possible that the harddrive is not running at its normal speed,|
freezing up or slowing down. Or has quit.
My computer took 20 min. to boot the other day.
I was watching the HDD activity indicator light,
and it would remain on, and not rapidly blinking.
Mechanical devices do have problems.
Harddrive manufacturers have software for download for testing HDD.
Watch for help from others.