I recently bought a Xbox Crystal edition with 1.6 revision board. I’m told the HDD has been upgraded to a 7200RPM 160gb seagate drive and it has an aladdin XT mod chip. It worked fairly well for a couple of days, crashing once or twice and showing error code 07 or 21 a couple of times. I have some tolerance for this kind of thing from old hardware. This morning, however, it was a nightmare to get working. Error codes 07 and 21 came up (mainly 07). It booted up a couple of times operating very slowly and not recognising the HDD. The times I have got it working, games have crashed after about 20 minutes claiming that the disc is damaged even though running from HDD. Any ideas!?!