Some games work- some games do not, what do I do?

[OnlineLove]

Hi, first time user, I really need help. It's been a few months, i booted up my Dreamcast today and it's not reading some of my games properly. It can't read Shenmue, giving an error that there's no game inside the drive. Space Channel 5 refuses to load, when I press play on the screen with Play, File, Music, Settings (soz idk what the name of it is) it will immediately boot back into the screen instead of playing the game. These are both games I have played on the system before, and I have save data for. Both disks are in good shape. I tried Crazy Taxi 2 and Soul Fighter and it worked perfectly.
What should I do? Is it something that can be repaired?

[Lorfarius]

Might be disc rot as you can't always see it.

[redjeff76]

clean your lens of the cd reader. Or else there is a good chance your GDROM drive is dying.