Wait, if the DVD drive is the only thing on the on the IDE channel and your system drive is on a SATA channel that does not really point towards a defective cable or drive. If a drive on an IDE channel is affecting performance of a drive on a SATA channel something is fubared either in the system drivers or in the chipset on the mobo itself. Idle devices on the IDE channels should not impact the performance of the SATA drive. BROKEN devices on the IDE channel should not affect the performance of devices on the SATA channel. Either the OS is screwing up all of your IO trying to deal with either messed up drivers, a messed up controller, or a messed up device (in order of probability) or the controller itself is messed up.
While it's possible that a messed up drive could cause a cascade of problems that could affect system performance this is not a problem PIO is causing, rather I would suspect that being stuck in PIO mode is just another symptom of a bigger problem.
When you checked the registry it was set to PIO, right? And you fixed it and when you booted up again it was already set to PIO even though you hadn't put any disks in the drive?
- Boot up with the DVD drive plugged in then check the system events log (right-click my computer > manage > event viewer > system) and check for errors pertaining to any drives or IO controllers (you might want to try doing this right after you've uninstalled the drivers).
- Update drivers and firmware for all drives and controllers (yes, I know, they worked before. But if they somehow became corrupt this should fix the problem without having to buy new hardware.) Also, when updating your BIOS reset it to default settings (you can tweak them again later after the system is at least working properly).
- Try a different optical IDE drive (preferably a DVD drive).
- Try a different cable with both the new drive and the old drive.
If none of that works I'd say try reinstalling windows as a last ditch effort (that shouldn't accomplish anything we haven't already done but it doesn't cost money and pretty much rules out software problems as the cause). You don't need to wipe the drive for this test, just install it in a different folder or partition or drive, (in reverse order of safety of your data) depending on your knowlege, comfort level, and how much trouble you're willing to go through. If that doesn't work seriously consider a new mobo and/or SATA optical drive (there are now a number of SATA optical drives available in the $20-$50 range).
This is an intriguing problem, keep us posted. You might have a magical drive here, the perfect thing to leave sitting out at a LAN party for someone to steal or as a gag gift :twisted:
Remember: Hardware that is working properly operates as designed. Broken hardware can do anything. I predict that the worlds first time machine will be a broken electronic appliance.