i’m not able to use the nuget manager in vs2012

You need to enable TLS 1.2, which is required since june 2020.

• start regedit.exe
• go to HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\.NETFramework\v4.0.30319
• create DWORDs SystemDefaultTlsVersions and SchUseStrongCrypto and set both to 1.

This will works since Windows 8, if you still use Windows 7, you need to enable TLS 1.2 first.