Broken references. c#

Hi. i expect that the answer can be trivial, but i am new to github and i couldn’t find solution myself.
When i clone my own repository from github, the new created VS solution has broken references. those basic references like System, System.Core etc. I can remove those references and add them anew but it doesn’t change anything.
the fun is that when i just copy the whole solution to the second computer it just work.