wesspicher

Here is a picture of my Christmas tree. It is one of those pre- lit ones that we have had for three years. I have been working on this thing for two days and have not had any luck getting it  to light up. I have replaced bulbs and used my limited electrical knowledge to trouble shoot the issue. I have one of those bulb testers and it also tells me if there is power on the string of lights. After replacing over40 bulbs it still looks like this. Any ideas on how to fix this silly thing? I am thinking about putting in some new strings of lights but it looks like it might be a ton of work.