You might try a different USB port, if available. Some ports are "current-limited" and don't put out enough juice for charging. Finding one on your computer is pretty much hit-or-miss, because most computer manufacturers don't disclose which is what in their documentation.

I have had good results with an aftermarket charge/data cable on my RAZR V3 by plugging it into a Compaq laptop and leaving the computer plugged in and in Standby mode (I just close the cover, which blanks the screen). It's a great feature when traveling, because it eliminates the bulk and weight of Yet Another Charger.