I had a similar problem years ago with several monitors. Old style monitors relied only on the soldered joint of the VGA port to hold the weight of the cable, after a few years, the joint could break and then the screen would be green or blue of one of the pins were not connecting.
So the problem is that the signal is not connecting from the motherboard into the monitor. So you will need to do trial and error to sort it out.
1. The monitor is faulty
Plug in to another monitor or display device with the same adapter, if the problem goes away then the problem is with the monitor or the VGA cable.
2. The connector is not plugging in properly
If the connector feels loose, then it may not be connecting properly. Try blowing in the connector to ensure there is no debris and see if you can get it to plug in correctly.
3. The adapter is faulty
You could have struck a bad batch of adapters and the second adapter could be faulty as well.
4. Loose or broken connection in the mac
If you have tried all that and there still is a problem, then the connector on the Macbook might be loose, or the main board or video card might be faulty. For this one you will need to call apple or an authorized repairer.
Well it turns out it was the adapter. I got a genuine one and it works just fine. – jasonh – 2009-07-24T03:39:10.833
Cool ! – Bruce McLeod – 2009-07-24T13:53:13.343
That's what I was afraid of. I already ruled out 1 and 2, so I think I'll have to give 3 a shot by getting a genuine Apple adapter. They'll have a hard time arguing that it's not the Macbook if I have three adapters with the same problem. – jasonh – 2009-07-23T08:49:49.363