Hi guys,
I would really appreciate it if someone can diagnose the following problem (or at least point me in the right direction to finding a solution

).
The problem: my laptop is cutting out - by this I mean when I am working on it it will simply cut out.
More on the problem: - it happens when two things occur:
1) I open one or two programs (these are not ram-busters either, MS Word or Fireworks/Dreamweaver).
2) And the fan (I think it's the fan!) really kicks in and you can hear it accellerate until it just cuts out and the whole thing switches off.
I am aware that this can be a symptom of overheating after hours of endless tasks and running programs however this is happening only a few minutes after switching it on!
It's not new, about three years old, but sees very little usage as the problem prohibits this!
Right, thanks very much guys - please help me!
Thanks!
Alex