It could be a clogged heatsink, open the base up and give it a hoover (yeah I know it creats static build up but its fucking easier than blowing it out) the heatsink is usually like a copper pipe with a smal radiator on the end, very common on Toshibas.
The other point is make sure the fans are enabled in the bios mate, enter the bios on bootup...F2 or del key are usually the ones to enter the bios....start by loading up default or optimum settings to make sure its all back to standard then go into the options to control the fan setting....this varies from bios to bios but usually is a setting of turn on temperature or power pc down at a certain temperature.
Check the actual level of temperature as the heatsink may have become dislodged from the chip...common on older systems and regrease it and reapply the heatsink. A normalish temp for a laptop is high 40's to mid 50's degrees c.
If that doesnt work then download speedfan
http://www.almico.com/sfdownload.php oe soemthing like that to check if the fan does actually come on and at what speed.
The other thing is that the fan has actually broken and needs replacing.
Hope this helps.
