bad disk - your player cannot read this type of disk or the disk is damaged - try another disk
there are bad connections to the drive - the data cable may be faulty or slightly loose at the rear of the drive or where it connects to the motherboard - - make sure the cable is fully pressed into its connections at either end and or swap the cable.
the laser or laser guidance on the drive has failed - a new drive will be required. New drives are less than twenty pounds.
Hands-on: Acer Predator Triton 700 review