Trying to remove heatsink, unscrewed fan cooler clamps and can't screw them back in

[LimboStudios]

Hello, I was cleaning my PC and removed the CPU heatsink to clean it off, as it didn't remove I accidentally unscrewed the parts designed to hold the heatsink in place, little plastic clamps.

https://ibb.co/fbBzWQ

I had removed some small silver screws that fit snugly into the clamps

https://ibb.co/cJgGBQ

However when I attempt to screw them back in, there doesn't seem to be any 'ridges' the screw can hold onto and I shined a light with my phone and there doesn't seem to be any 'backplate' where the screws can fit in.

Did I mess up royally? Is there a way to screw them back in? My Motherboard is an ASUSM5A99FX

 

[coozie7]

From what I can see the CPU mounting backplate is retained by 4 small nuts that look captive https://www.newegg.com/Product/Product.aspx?Item=9SIA85V4405098
Click on the little box with the three dots in it, located to the right of the 4 small images below the main image, then select the motherboard rear image and zoom in on the backplate, you can clearly see 4 hexagonal openings in the corners, my guess is that those nuts have become dislodged or have even dropped out, remove the other case side panel to locate them.