Usually this is caused by the battery having gone flat when the laptop was put on standby rather than being fully shut down. To fix this do the following:
- Plug in laptop and boot up.
- Log in with username and password.
- Shut the laptop down and leave power supply pugged in.
- After a couple of minutes the battery charge light should come on.
- Now switch on laptop.
- Battery indicator should be working and show a percentage.
Sometimes no icons will be displayed on the desktop.
This is also caused by the battery going flat on standby or by the shut down after standby not working correctly. Usually rebooting will fix this.