Oggin,
Assuming your problems continue and it is not a virus/duff software, there is another test you can run. Most PCs have inbuilt temperature sensors. A useful free programme for finding what is going on heat wise inside your PC is:
Speedfan.
Re hoovering out the dust - a word of
Warning.
Hoover hoses being attached to rotating fans can carry a lot of static, putting one inside your PC can result in a static discharge with disasterous results for static sensitive components. Keep the hose as far from the PC as you can.
Hope this helps
EG