Please select a valid startup item

It might be the case that you have opened your project using

File->Open->Folder

Use the right method to open your project using

File->Open->Project/Solution

or

File->Open->Website

File > New > Project From existing code. Select type of project > Next. Enter project name > Finish.

I went to File > Open > project/Solution and found the ".sln" file. I clicked on it and then pressed open and it worked for me. Just spent ages trying to figure this out!

Regards,

Open Visual Studio ------------------

1. Click File
2. Click Open
3. Open as Web Sites

Another method

1. Click File
2. Click Open
3. Open as Project