An iPod may not charge because of an underpowered USB port, an indirect connection, the FireWire isn't powered or is overused, the computer isn't active, Windows 2000 is installed or the iPod is locked up. There are many reasons why an iPod may not charge, and professional repair may be necessary if troubleshooting doesn't yield results. Repair can be arranged at Apple's support website.
The most common reason why an iPod isn't charging is because the USB port isn't putting out enough power to adequately charge the device. This can be solved by connecting the iPod to a USB AC-power adapter, or directly to the computer. Some Windows PC computers don't have powered FireWire ports, which are necessary for charging. Too many devices attached to the FireWire can also decrease charging capabilities.
With the exception of some Macintosh devices, computers must be active to charge an iPod. Configure the settings to keep the computer active longer if it's going into sleep mode automatically during charging sessions.
The iPod also can't charge if it's locked up. When this happens, reset the iPod. Although certain custom settings may need to be reconfigured, all files do remain saved. Using Windows 2000 is another common reason why an iPod may not charge. Consult Apple support for information on properly charging with Windows 2000.