Well, I just downloaded Unity 5.3.1f1 to my Windows 7 computer. It has 4GB if RAM, 3GHz Intel Pentium CPU, and 64-bit OS. When I clicked on the Unity shortcut, a gray screen appeared, like this: I waited a lot of time, and it didn't open. Does that mean that my computer it to weak to run the program? If not, how do I fix this?
I don't know what exactly the issue is, but if I had to take a guess it's something to do with the license screen that comes up when you start (ie. Unity connects to the internet to validate your license.) Certainly your computer is plenty powerful to run Unity.
I have the same problem. I've installed and unistalled unity a lot of times and I've tried to restore OS but this issue continues. My laptop has 4 GB RAM, intel core i7 Q 720 1.60 GHz and Windows 10 64 bits. One year ago I worked with Unity in this laptop and I didn't have any problems.
You guys should contact Unity support directly, not just this forum. They usually respond quickly to technical problems with installing the software.