Windows can give this error for a variety of reasons. It is described as "Device can not start", which can mean several things. Generally, this error message is indicating a problem in one of the areas below:
A cabling problem. A failure in the USB or FireWire cable is the most common cause. Replace the cable.
A power problem. This can mean a faulty external power supply, or on bus-powered devices, the computer isn't providing enough power. Try a different power supply (or different computer for mobile drives.)
A Windows problem. Driver issues, invasive security programs, or physically broken USB ports are another common cause. Instead of attempting to fix this problem right away, try a different computer to see if the problem follows the drive.