My PC won't boot

Late last night I was working on a PC that had been bought round for me to look at, symptoms where -
1. Won't always boot-up, press the power button doesn't seem to turn the system on.
2. When it does come on, the fans inside are noisy and rattly. Almost like there is something trapped in them.
3. Before it had died completely the system had been complaining of CPU errors and turning its self off due to over heating.

So I pulls it apart having a look at the memory and processor, on extracting the fan and heat sink I notice its very dusty. To the point that when I look though the fins at the side I can see any light, so I pop the fan off and on the right is what I discover. Urgh! No wonder it don't work, even when I pop a spare CPU and fan it it won't start. So the CPU and motherboard are toast and I don't have any spares. My next job is test the memory, graphics card and hard drive, if I can recover there data. Good job they are looking at getting a laptop.