macpro4,1 northbridge too hot & missing screw

Hello

My Mac Pro is a Nehalem Quad-Core Intel 2,26 GHz (macpro4,1) Early 2009

I got a big problem, it shut down my mac (krash)

I got since the 1st minute of boot the Northbridge go to 128°C / 260°F

I try the official APPLE HARDWARE TEST and get the error code (from the short & fast test) =

4SNS / 1 / 40000000: TNOD-127.875

impossible to run the long test, the computer krash before the end...

when I open the computer to clean up the dust

I saw a spring (metal spiral) alone... and then I saw what I think is a missing screw near the radiator, which make sense with the high temperature I got.

but the strange thing is HOW the **** the screw is removed by hitself ???!!

here is a photo of the processor tray where I believe the screw is missing

is anybody can confirm it to m, please ?

So has I only got the spring and I can't find the screw.

Please help me to fix/repair my mac pro.

Can anyone tell me or show me a photo of the same part. to see if there's something in this hole ?!

Where I can find this king of screw ??

How can I repair this ?

Is anybody have seen something like that ?? ==> missing screw without anybody touch it ? (I only add RAM to this part of my computer a never open it...)

SOOOOO STRANGE !!!!

PLEASE HELP !!

Thanks in advance !