Shuts down randomly.
Makes ticking or clicking sounds.
LCD shows coloured lines when booting up.
LCD display fails, or flickers
Makes a high-pitched whining noise.
CD/DVD drive scratches disks.
WiFi connection is poor quality and/or keeps dropping.
Trackpad is unresponsive.
Black screen of death.
Slows down considerably when playing video.
Symptoms include: 'flashing folder' with ? symbol; spinning 'beachball'; white screen.
Knocking a drink onto the keyboard.
Dropping the machine - or something onto the machine.