Hello, 

first of all do you mean Whatsapp for PC, if yes then here is a bit explanation.

For downloading All you need is Bluestacks as colleen had mentioned above, but that as well some times give error..

Reason 1: Download Broke up ( Re download it and it might solve the issue)

Reason 2: Your PC is without Graphics Gard or with low memory ( Please not to installl Bluestacks you need Good Ram and Graphics Card - Still Solutions is Available)

Reason 3: Instead of windows version you might have downloaded Mac version...

and so on what i know at present.

All i have found is a interesting post with a video tutorials as well a download link if you have Graphics issue...   Download and Install Whatsapp for PC 

I have found that article a nice write up, even through whatsapp download is pretty easy just download the correct download file, instead of not reading and downloading a wrong on....

Hope all your doubts are clear now...