Unity 4.2 won't run after I download free version. NSIS Error

Hi,

Im just starting to try building my own sandbox game but as soon as I download Unity 4.2 it will not run on my computer. It reads that it may be due to incomplete download and damaged media.

I am wanting to try building a GTA type sandbox game. Since the Unity 4.2 does not seem to work, is there a way I can fix it, or could an older version of Unity also work?

Thank you

 

Have you tried uninstalling Unity, deleting the downloaded file, deleting your browser cache and then downloading installing it again?

FYI Older version are located here http://unity3d.com/unity/download/archive

 

I've tried all that and have read other complaints where they try to download older versions and get the NSIS Error. I have tried to download v.4.2.1 on both Windows 7 and Windows 8 and I still get the same NSIS Error. On my Windows 8 computer I turned everything off and left my computer open to viruses. I turned off SmartScreen. I also noticed that the program is 880 MB and only 777 MB downloaded. The program has been set up to take over 12 hours to download 880 MB, I've downloaded other programs with the same amount of MB in less time. FIX THE PROBLEM.

 

I just downloaded the 4.2.1 installer (UnitySetup-4.2.1.exe), and it was 923471832 bytes in size. An MD5 hash for the download gave 78ac53ca13134a24327a8d157ffa83a7. Please check that the installer you fetched was the same size, and gave the same MD5 hash. If either number is different, you have a corrupted download.

 

Every time it only shows 881MB. I don't know where you're getting the other numbers from. Both of my computers are Hewlett Packard.