I'm not a very big Fan of Fan-problems (but well, who is

)
Ok, so here's the problem:
since a few days ago, one Fan started to make a noise in my computer (as is its stuck but still trying to work (wich it halfly does)
Now is the problem: what should i do: - probably have to bring it to the shop for a new fan or so (atleast that i'm afraid will have to be done.
But i don't know either what the fan is for, so i thought, maybe post here and see if any of you know.
Just in case i made a few pics of it as my description prolly is more cryptical then informational.
Description: the fan is in a little box on the mobo (not close to the CPU, more or less behind the video card). The only thing the mobo manual says is (atleast the little square where i think the fan is placed) "nforce4 SLI".
I was also wondering if it was anything critical, that should be threated right away or something that just needs to be taken care of sometime.

and
