On my laptop (from which I am posting now), right clicking the 'Primary' or 'Secondary' IDE channels and going to 'Advanced Settings' tells me which transfer mode is in use. For HDDs, UDMA is the default mode.
See this screenshot I just took.
In any case, I've never heard of a faulty drive fixing itself, so it's best you backup as soon as possible.
You can copy over your files (personal data files, not system files) to one of the other two drives (if you know that they're reliable) or to an external HDD until you replace the faulty HDD. Then you can copy them back on to the new replacement drive
If the faulty HDD contains your Operating system, then you'll have reinstall the OS and whatever programs you use on your new HDD. You cannot drag-copy an existing OS over to a new drive, but you can image it (not recommended, if the source drive itself is faulty).
Hope this helps