design view not working

The reason behind not showing design view is the only that you have deleted some control from the page but the reference of that control is still present in your design page.

If the case is same what I have guessed then please open design file code and delete the reference of that control which you have deleted from the view page and your issue will be resolved.

If this is not the case then please provide some more detail so that it can helpful in identifying the exact problem.

Hi.

i don't think any issue with your code but please restart you VS 2015 and check it.

Thanks.