top half of screen is darker with blue color lines running down

How do I fix it? Can I? Outside screen is fine.
HTC thunderbolt

I think this is a hardware issue, maybe water got inside the phone? If you're feeling adventurous, you could try replacing the screen ([Only registered and activated users can see links. Click Here To Register...]) using [Only registered and activated users can see links. Click Here To Register...]. If not, I think you'll just have to buy a new phone or put up with it.

Yea, probably hardware. To be sure, you can factory reset.

If that doesn't fix it, is it under warranty, or, at least insurance? If so, might be time for a new phone.