Im assuming here that you are using win2k or XP.
For some reason certain optical drives are touchy with 2k or XP.
Things you should try to fix the issue:
1. reverse the drive sequence master -> slave and slave -> master.
2. replace the IDE cable.
3. Remove the drive from the devices page and reinstall it.
4. install or reinstall the latest Chipset drivers
5. delete the IDE channel from the devices page and reinstall it also.
I know what its like. I had a pioneer 106S dvd that mysteriously would drop out of UDMA mode every now and again. Most times resetting udma and rebooting worked, but once i had to do just about all of those things on my list to get UDMA up again.
<b><i>The Very Hungry Caterpillar</i> - George W. Bush's favorite childhood book.
Note: This book was first published a year after Mr Bush graduated from College.</b>