R problem Resolving Host Github: curl::curl_fetch_memory(url, handle = h)

[PHDism]

have the following problem downloading package from github:

devtools::install_github('walkerke/tigris') Error in
curl::curl_fetch_memory(url, handle = h) : Could not resolve host:
api.github.com

I was able to do this successfully last night, but then I had some other issues downloading some shapefiles from census. Meanwhile downloading package from github did work. So here is what I did:

1. I unchecked Use IE library/proxy for HTTP and I tried to create a new .renviron file with proxy. that did not solve the problem with census.
2. I re-checked IE proxy setting, and I deleted the .renviron file that I created (going back to how it was). Now I started having problem with github (resolving host).
3. I removed CURL and HTTR. I reinstalled them. That did not help
4. I deleted CURL and HTTR folder libraries manually and reinstalled them. that did not help.
5. I had R and R studio completely uninstalled, deleted folders and then installed. However I still get that error.

"curl::curl_fetch_memory(url, handle = h) : Could not resolve host: api.github.com".

I am just trying to get refresh everything I can, to get to the point I was last night when I could do successfully without errors resolving host the following:

devtools::install_github('walkerke/tigris')

Back when this worked (yesterday), I did not have any special proxy settings, and I did not have .renviron file. This stopped working when I created and then deleted .renviron file.

What else can I do?

Thank you for your help!