I have an error when I start PHP 7 on Windows. When I run
Unable to start the program as VCRUNTIME140.dll is missing on your computer. Try reinstalling the program to fix this problem.
I missed this too, and it held me up for a while. The answer marked as "the answer" does point in the right direction for the solution, but I thought I'd add this answer too.
On the side bar of the PHP 7 alpha download page, it does say this:
VC9, VC11 & VC14 More recent versions of PHP are built with VC9, VC11 or VC14 (Visual Studio 2008, 2012 or 2015 compiler respectively) and include improvements in performance and stability.
The VC11 builds require to have the Visual C++ Redistributable for Visual Studio 2012 x86 or x64 installed
The VC14 builds require to have the Visual C++ Redistributable for Visual Studio 2015 x86 or x64 installed
(Update: there's been a problem with some of those links, so the files are also available from softpedia).
In the case of the PHP 7 alpha, it's the last option that's required.
I think that the placement of this information is poor, as it's kind of marginalised (ie: it's basically literally in the margin!) whereas it's actually critical for the software to run.
I documented my experiences of getting PHP 7 alpha up and running on Windows 8.1, and it covers some more symptoms that might crop up. They're out of scope for this question but might help other people so I'll include the link: "PHP: getting PHP7 alpha running on Windows 8.1".
Other symptom of this issue:
(I include those for googleability).