Tv beginning to flash green with horizontal white lines

From your description it sounds like a bad picture tube. The lines are called retrace lines. There is a small chance that a component on the small board that connects to the neck of the tube may be bad. Without model number information it is very difficult so say further. Some picture tubes can be re-jeuvenated with the appropriate machine ( at a TV repar shop)
If you feel adventurous and are careful you might try GENTLY tapping the neck of the tube and see if picture improves/goes out. If the tapping does change the picture it is definitely the tube