[Tom Fifield]

What is your system?
It sounds like a computer problem, it could be some ram went bad or your video card, the green line makes me think card. The start up thing makes me think bad Ram or card or worse. But it could be your OS has been corrupted in that case you would need to reinstall or fix with the install DVD.
First thing to do is as you start up and zap your pram, then repair permissions, run Mac Janitor (a free down load). Then do the systems check. Do a systems check and it will look at every thing including your video card you may want to bring it in.
Hopefully you backed up every thing.