[shjoshi]

I suspect your R and RStudio installation must be fine. Before you try uninstall/reinstall, can you try running R as an Administrator?

Look at this link,

Then post the output of .libPaths().

If you ran RStudio as an administrator, try installing devtools.
install.packages("devtools")

Note devtools is enclosed in double quotes.
When typing the install.package command above, please type it manually in your R console, since copying pasting from the web may garble some characters.