First thing to do...go into device mgr/system/performance....see if any drives are in the compatability mode. Ignore any referances to the A drive. If the C drive is in compatability, that's at least one of your problems.
In device manager, is the secondary IDE device shown? It should not show up. If It's there, highlite the VIA controller, then remove it, reboot, see what shows up. Under properties of the controller, settings, specify Primary IDE only. Reboot....if the secondary IDE device is still there, try this: reinstall the 4-in-1 driver 4.29v...only this time, during the install, about the 4th screen or so, remove vendor support for the ATAPI controller (I think that's what it says)..Reboot again. Go back to the controller and specify again Primary IDE only...reboot. The secondary controller should now be gone. This is a long procedure, many reboots, a few crashes. After it's all over...you should have a VIA controller and the Primary IDE channel only in device manager. Now try again to enable DMA for your drive. If it still won't enable, I think it's time for a new drive. Keep your eyes open for the next 4-in-1 driver "coming soon". I think this latest 4-in-1 caused some of these types of problems.
In device manager the hard drive and the sandisk are called "Generic type 47". Ignore any referance to the A drive...It's a phantom device on this computer...Windows always thinks there is a floppy. Doesn't hurt anything however. I don't thing any BIOS setting changes will have any effect on this problem.