Realtek network controller not found

hey,

I am facing this trouble since i purchased this laptop i have a Dell vostro 2520 running on windows 8 pro X64,

so the problem is that whenever i try to install drivers for Ethernet which i downloaded from the drivers and download section of this website it gives me an error "Realtek network controller was not found If in deep sleep mode please plug in the cable" now the thing is that it cannot be a problem in my windows as i was running on windows til few days ago, I got the same problem in windows 7 as well,

I have searched everywhere and i have tried almost every solution i got but to no avail the problem still persist  and i cannot use LAN for Internet or file transfers,

P.S:-  I looked for the adapter under the "control panel\system and security\system\device manager\Network adapters\" But didn't found anything there saying Ethernet or  something like that.

I am uploading the screenshots of the problem i am facing, I hope it helps.

thanks for any help in advance