The "Compile" button is grayed out, even after rebooting laptop and restarting Unreal Engine 4.7.3

[This is the UE4 tutorial I am following at the moment.][1]

This is what is shown in the Editor.


This warning is telling me something deprecated that I am not sure about just by following the tutorials.

Why couldn’t I no longer compile? I was able to compile yesterday, so I am confused.

Edit: I am using Unreal Engine 4.7.3. Operating system is Windows 8.1.

Update (3/19/2015, 7:53pm):

After I restarted my machine, and booted up the Unreal Engine 4, the “Compile” button at the top is still grayed out. I have no idea why it is grayed out.

Call me paranoid, but I feel like wanting to fix this issue.

I went ahead and re-install Unreal Engine 4.

Now it is fixed.