The battery may need to be re-seated. Try rebooting the computer without, then with the battery.
1. Power down the laptop, unplug the AC power adapter, and remove the battery. Then plug the AC adapter back in and boot the laptop
2. If step 1 is okay, then power down the laptop again, unplug the power adapter, and reinsert the battery. Plug the AC power adapter back in and boot the laptop
If the unit still does not charge, then it could be a problem with the power management software. In order to correct the problem:
1. Click Start and type "device" in the search field, then select Device Manager
2. Double-click Batteries
3. Right-click the Microsoft ACPI Compliant Control Method Battery listing and select Scan for hardware changes
If this does not work, then
3. Right-click the Microsoft ACPI Compliant Control Method Battery listing, and select Uninstall.
WARNING: Do not remove the Microsoft AC Adapter driver or any other ACPI compliant driver
4. On the Device Manager taskbar, click Scan for hardware changes