Fatal error connect to github

I suddenly found I cannot push/pull from github anymore, always get the error:

FATAL ERROR: Network error: Connection timed out
fatal: The remote end hung up unexpectedly

This happens after I've installed TortoiseGit on my laptop. However it doesn't help to remove that program from my computer. In the end I found there is an environment variable named "GIT_SSH" point to "C:\tools\PLINK.exe". After I changed it to "C:\apps\Git\bin\ssh.exe" the github connection come back.