Could not find a version that satisfies the requirement tensorflow
Uninstalling Python and then reinstalling solved my issue and I was able to successfully install TensorFlow.
I installed the latest version of Python (3.6.4 64-bit) and the latest version of PyCharm (2017.3.3 64-bit). Then I installed some modules in PyCharm (Numpy, Pandas, etc), but when I tried installing Tensorflow it didn't install, and I got the error message: 

Could not find a version that satisfies the requirement TensorFlow (from versions: )
      No matching distribution found for TensorFlow.

Then I tried installing TensorFlow from the command prompt and I got the same error message.
I did however successfully install tflearn. 
I also installed Python 2.7, but I got the same error message again. I googled the error and tried some of the things which were suggested to other people, but nothing worked (this included installing Flask). 
How can I install Tensorflow? Thanks.