Re: it doesn't tighten against the PCB or the bottom of the leg I thought the heatsink screws are mounted to M3 threaded nuts of a backplate slightly protruding through the motherboard.  during the tightening steps you would feel one of the 4 screws reaching end of travel, meaning it has met sudden hard resistance, then the rest three screws do the same.  the resistance may come from the heatsink cold plate touching the CPU IHS (heatspreader).  general advice is not to overtighten beyond this step to ensure a good thermal contact but avoid unnecessary stress pressure on the cpu. Re: C957N another vendor shows pic of this part without washer.  when you tighten the screws I suppose the screws would gradually protrude further and further out of the washer into the M3 threaded nuts of mobo back plate. [IMAGE] [IMAGE] I think the washer and plastic enclosure of screws are all part of heatsink housing.  As you tighten the spring loaded screws, the spring inside the plastic enclosure is then tightened which applies elastic pressure on the heatsink body pushing it down closer n closer towards cpu.  In other words, the screws themselves do not directly work on the heatsink, but via the coil spring in the enclosure. the washer is there to support the bottom of spring. In some design of heatsink when there is no washer, the plastic enclosure itself has a floor to support the spring.  Either way, the spring must be supported at bottom so when the screw is tightened on the top, the spring can be squeezed effectively so that it can push the heatsink down. if for some reason the plastic enclosure is damaged (sounds like in your case), the elastic pressure from spring to the heatsink may get compromised, which might explain your puzzle.  HTH.  
Greetings Dell folks, I guess I'm a bit of a Dell fan, as 3 XPS units myself and got an XPS for my GF. The other day I bought a project Inspiron 570 with an Athlon II processor. I just wanted it as a test mule of sorts for verifying backup viability without having to mess around with removing the HDD's from my own XPS 8300, Maybe a lame idea, but it seems to make sense. Anyway, I bought the unit w/o RAM and "possibly needing a PSU" (You know when they say "possible" that it means probable.). So I looked into getting the right type and amount of RAM and a working PSU. With the existing "possibly bad" PSU, the switch light would light up but blink amber. I read on here somewhere that this indicates a bad PSU. While I awaited these parts I wanted to see what was under the CPU fan so I removed it to check it out. It is indeed an Athlon II as was mentioned by seller of unit. What's weird is that as soon as I started loosening the screws I noticed that the bottom of the plastic legs on the sink/fan frame were broken. I did not force any of them to cause this. Most of the fan/sink setups that I see for this model Inspiron have plastic legs with the screw protruding from the bottom, which somehow engages the shock springs within the lets. The one I have has round retaining clips/washers that lock into a groove around the bottom of the screws. As I work with it, I can't for the life of me figure out how the springs get engaged at all. When the screws bottom out to the PCB, the clip/washer is loose between its groove and the PCB. This would seem to guarantee some sort of rattle once the machine starts up. Was this an early design that was changed due to problems? I also read on the forum here that there is a tightening sequence of the screws that is indicated by marks at the threaded inserts in the PCB. I see an H4, H5, H6, and H7 there. Does this mean that I tight them starting with H4?  [IMAGE]
Confusing design on CPU cooling fan/sink on Inspiron 570.