install.packages("Hmisc")
Warning in install.packages : unable to access index for repository https://cran.rstudio.com/src/contrib:
cannot open URL 'https://cran.rstudio.com/src/contrib/PACKAGES' Installing package into
‘C:/Users/Tushant/Documents/R/win-library/3.4’ (as ‘lib’ is unspecified)
Warning in install.packages : unable to access index for repository https://cran.rstudio.com/src/contrib:
cannot open URL 'https://cran.rstudio.com/src/contrib/PACKAGES'
Warning in install.packages : package ‘Hmisc’ is not available (for R version 3.4.2)
Warning in install.packages : unable to access index for repository https://cran.rstudio.com/bin/windows/contrib/3.4:
cannot open URL 'https://cran.rstudio.com/bin/windows/contrib/3.4/PACKAGES'
I don't know if you are interest of the answer at your problem, but today I had the same your problem and I resolved this with the download the last version of R software.