How do I know which cpu fan will be cool enough for my pc on ebay?

I just bought one is was fairly cheap I have a multicore processor each core runs at 4000 I bount a cheap fan and basically my pc shts down if i run too many things at once or if the room is too warm. The fan keeps going even after I turn it off sometimes!? It keeps restarting the switching itself off after... show more I just bought one is was fairly cheap I have a multicore processor each core runs at 4000

I bount a cheap fan and basically my pc shts down if i run too many things at once or if the room is too warm.

The fan keeps going even after I turn it off sometimes!?

It keeps restarting the switching itself off after the initial switch off im not sure if thats normal? (need to leave it off for a while before it comes back on to cool down)
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