Common causes are:
Bad USB cable.
Insufficient power.
Windows driver or USB problem.
The next best step is to do a series of physical tests to see if the problem can be isolated to a small component, rather than the drive itself.
Change the USB cable with a different one.
If the drive is bus-powered, use the USB power sharing cable. For normal drives, try using a different external power supply from a different LaCie (if possible.)
Move the drive to a different computer.