how do i fix my ipod touch 4th gen with vertical lines on the screen???

Have you tried a reset?

Hold the Sleep and Home button down until you see the Apple logo.

Try:

- Reset the iOS device. Nothing will be lost

Reset iOS device: Hold down the On/Off button and the Home button at the same time for at

least ten seconds, until the Apple logo appears.

- Restore from backup. See:

iOS: How to back up

- Restore to factory settings/new iOS device.

If still problem, make an appointment at the Genius Bar of an Apple store since it appears you have a hardware problem.

Apple Retail Store - Genius Bar