Check the CD's. When these are copies, burned in a computer, your player could have problems playing them. Not all players can play self burned CD's. An original CD has a metallic reflective layer, with a high contrast on reflectivity. The self burned CD's only have a dye, where a laser changes the colour on the same places as the pits are on a real CD. But the dye gives less contrast. When on the player is no logo, compatible with CD-R, you can't expect it will play these. When it won't play real CD's, perhaps you could try a cleaning CD and try playing a CD again.
For that you can buy a cleaning CD, with a soft brush. dust and a coating from smoke can be removed. If the laser is defect, not aligned or not calibrated, don't try to cure that.
The brush on the CD looks like this: