The make is a compaq presario around 6 years old and running xp home.
woodchip..I think it may be the fan becasue the laptop feels quite hot underneath, I didn't realise it might be the harddrive, what could be wrong with that.
Thank you all for your help. Just one last thing, if this repair is too expensive then my friend who is not computer savvy will buy another laptop, but she wants to keep XP home on the new one as she is used to it. Can we buy a new laptop with XP on it?.....
After six years of use it is very likely you have a lot of dust/fluff around the fan an cooling ducts/fins as spiderlegz indicates. You really have only two options, to do it yourself or get it serviced.
If you want to have a go yourself, there is a video which may help and a simple suggestion here.
Personally I would be tempted to do the minimum of disassembly and use a vacuum cleaner to remove as much dust/fluff as possible. Obviously the laptop must be switched off and care taken when using the vacuum not to do any damage.