Just installed latest Unity and get internal compiler error-will not run at all

Hi, I just downloaded and installed the latest version of Unity, but it will not run anything, it will not even enter play mode with an empty scene. I keep getting this compiler error by simple running Unity-

“Could not start compilationWin32Exception: ApplicationName=‘J:/programs/Unity/Editor/Data/Mono\bin\mono.exe’,”

and
“compilation failed because the compiler couldn’t be executed!”

and more detailed info displayed from the first error-

“Could not start compilationWin32Exception: ApplicationName=‘J:/programs/Unity/Editor/Data/Mono\bin\mono.exe’, CommandLine=‘J:/programs/Unity/Editor/Data/Mono\lib/mono/unity\smcs.exe @Temp/UnityTempFile-4dffa9d09e9614548af7cee93a97c0e0’, CurrentDirectory=‘C:/Users/Mark/Documents/CaptainBlaster/Assets/…’
System.Diagnostics.Process.Start_noshell (System.Diagnostics.ProcessStartInfo startInfo, System.Diagnostics.Process process)
System.Diagnostics.Process.Start_common (System.Diagnostics.ProcessStartInfo startInfo, System.Diagnostics.Process process)
System.Diagnostics.Process.Start ()
(wrapper remoting-invoke-with-check) System.Diagnostics.Process:Start ()
UnityEditor.Utils.Program.Start () (at C:/buildslave/unity/build/Editor/Mono/Utils/Program.cs:33)
UnityEditor.Scripting.Compilers.MonoScriptCompilerBase.StartCompiler (BuildTarget target, System.String compiler, System.Collections.Generic.List1 arguments, Boolean setMonoEnvironmentVariables) (at C:/buildslave/unity/build/Editor/Mono/Scripting/Compilers/MonoScriptCompilerBase.cs:32) UnityEditor.Scripting.Compilers.MonoScriptCompilerBase.StartCompiler (BuildTarget target, System.String compiler, System.Collections.Generic.List1 arguments) (at C:/buildslave/unity/build/Editor/Mono/Scripting/Compilers/MonoScriptCompilerBase.cs:20)
UnityEditor.Scripting.Compilers.MonoCSharpCompiler.StartCompiler () (at C:/buildslave/unity/build/Editor/Mono/Scripting/Compilers/MonoCSharpCompiler.cs:44)
UnityEditor.Scripting.Compilers.ScriptCompilerBase.BeginCompiling () (at C:/buildslave/unity/build/Editor/Mono/Scripting/Compilers/ScriptCompilerBase.cs:47)”

I think it has something to do with the fact that the Mono updated didn’t install correctly, and I have tried reinstalling it three times and the same thing happens, so I am at a loss as to how to fix it.

This doesn’t just happen with one scene or project, it is happening with everything, even new empty projects.

I figured out what was going on. Norton thought mono.exe was a virus and quarantined it. Even after I turned network protection off it still would not install, it was being quarantined by something called SONAR protection, so I had to go in and un-quarantine it.