Computer makes loud fan noise, then turns itself off and makes clicking?

Turned computer on the other day and it was making a very loud noise, like a fan. It kept on doing that, then it turned itself off and was making a clicking noise. Pressing the power button did nothing, so I had to unplug it.
I can still use it but everytime I turn it off it makes the clicking noise. The fan noise does come on most times too during use.

Hannah
March 2006