Installing of toolchains could take some time depending on the speed of your Internet connection.
If repeated attempts and a long waiting does not help, try to install toolchains manually. Here is detailed instruction: Can I manualy install the toolchain?.
If this does not help, try to mark “Compile in the cloud” option in “Upload to Arduino” dialog and please write some information to help us make it working for you:
- which OS you are using,
- Board model,
- which port did you selected,
- does compilation in the cloud helped?
Thanks!