==> Dreamcast Problem!!! HELP...

[wasabi]

Recently, I bought a used dreamcast console. When I play after an hour, there're few games (backups such as crazy taxi 2) that no longer boot or not detected by the console at all. Sometimes, during loading or gameplay, it frooze or it takes a long time. Do any of you know what's the problem??? Is it the laser len is dirty? Something wrong with the motor? Any thing I can do to fix this?

Any comments are appreciated!!! Thanks...