fan not working

ok one of my friends wants me to look at a pc for them.they tell me the fan is not working. i dont know if it is the cpu fan or the power supply fan.heres the ? when i open this up with the power on should the cpu and the power supply fan be running at all times??and if they give me just the tower could i use one of my power supply cords . they look the same on my gateway and my compaq.one more ? were is a good site for buying cpu fans and new power supplys???????
also if the cpu fan was not running it must be shot?????? and if it was cpu fan woulnt it burn up the cpu by now .thank for any help on this

 

can anyone help on this????????????????????????

 

first off the power cords should be the same if it fits it should work
second what is the pc doing is it shutting down do to heat or what
and newegg is about the best place for anything computer related but if the psu fan isnt working ull have to buy new psu but if the cpu fan isnt working i would think that the pc would turn itself off due to heat but like i said what are the symptoms or do they just not hear fans

but if u dont like newegg just google for power supplies and cpu fans

 

i am not sure what simptoms there are just yet . ? is the cpu fan and power supply fan allways to be on ?????

 

yes they are, just varied speeds but always on.

 

so if i plug it in and one of the two is not running then thats the problem ????????

 

Yep, should be.

 

ok here is another ?????????? i hear there are water cooled fans?
can you give me some links on different fans (pics) like anthalon,and pentium.thank for any pics