Enable Button when score is greater than 1000

Questions & Answers
1

How can I enable button when my score is greater than 1000???

2

The simplest way is to just put an 'if' statement inside OnGUI, something like this:

void OnGui()
{
    if (score > 1000)
    {
        GUI.Button( /*...*/ );
    }
}

http://unity3d.com/support/documentation/ScriptReference/GUI.Button.html