|Try booting to a bootable factory CD or DVD to see if the drive can read them then. If so, then it may be a OS issue. If the disks can't be accessed at boot then the following may apply.|
Is the drive properly identified by model in Device Manager?
There are two lasers in combo drives. One for each type of disk. The power output is variable with less power required to read than to write.
The lasers may be wearing out, which is common. Or the lenses are dirty, impeding the passage of the light. The fact that both are affected may indicate the lenses are the issue. There are lens cleaning kits available. If that doesn't solve the problem then you may need to replace the drive.