Yes, it could be the problem. Look on the back of the drive, there will be 8 pins in their own box (perhaps with a white plastic thing [a jumper]). Next, look at the top of the HDU and you'll see that there are options for the HDU using these pins and positioning the plastic jumper on the correct pins. Look for something like 'enable SATA 150MB/s only mode' and set the jumper across the pins it states. There is a diagram to show you exactly. Try this and then replace the disk and see if it works.
