After i tun my ipod touch on is stays on a black screen

Tweaking the brightness settings on your iPod touch saves your eyes from unnecessary strain.

Changing the brightness settings can be done quickly if you're on the go.

Adjusting the brightness of the screen can make the device brighter if you're in a dark environment or darker if you're in a bright environment.

Alternatively, you can set the device to automatically adjust to the level of brightness it's exposed to.

Press the "Home" button to return to your iPod touch's home screen.

Tap the "Settings" app.

Tap "Brightness." A scroll bar appears at the top of the screen.

Press and hold your finger against the circle on the scroll bar.

Drag your finger to the right to brighten the screen and to the left to darken the screen.

The screen's brightness will change as you move the circle.

Alternatively, tap the ON/OFF toggle to the right of Auto-Brightness to have the device automatically adjust itself based on the detected brightness level.

Tap the "Home" button just beneath the iPod touch home screen to save your changes and return to the device's home screen.
if this is not or cant fix the problem you might have restore it to factory settings

You can use iTunes to restore iPod Touch software.

Apple recommends using the latest version of iTunes to complete this process.

Follow these steps to get the latest version of iTunes and restore your iPod Touch software.

Back up your iPod Touch's data to your computer before the restore to prevent losing data.

You'll need to reinstall it after the restore process.

Connect to the Internet and install the latest version of iTunes from the Apple website.

Make sure your iPod Touch is connected to your computer.

Pick "iPod Touch" in the Source pane of the iTunes program.

Click on the Summary tab.

Choose "Check for Update."

Select "Restore" and follow the instructions to finish restoring your iPod Touch.

although it does sound like a hardware problem with the ribbon cable leads so if this fails and you are tech savy you could try to open it up and to have a look

hope this helps