what do i do if i cant restore my ipod touch 4g.

Placing your device into recovery mode

Follow these steps to place your iOS device into recovery mode. If your iOS device is already in recovery mode, you can proceed immediately to step 6.

1. Disconnect the USB cable from the iPhone, iPad, or iPod touch, but leave the other end of the cable connected to your computer's USB port.
2. Turn off the device: Press and hold the Sleep/Wake button for a few seconds until the red slider appears, then slide the slider. Wait for the device to turn off.

   If you cannot turn off the device using the slider, press and hold the Sleep/Wake and Home buttons at the same time. When the device turns off, release the Sleep/Wake and Home buttons.

3. While pressing and holding the Home button, reconnect the USB cable to the device. The device should turn on.
   Note: If you see the screen pictured below, let the device charge for at least ten minutes to ensure that the battery has some charge, and then start with step 2 again.
   
4. Continue holding the Home button until you see the "Connect to iTunes" screen. When this screen appears you can release the Home button:
   
5. If necessary, open iTunes. You should see the following "recovery mode" alert:
   
6. Use iTunes to restore the device.

What happens when you try? Error message?

See:

iTunes: Specific update-and-restore error messages and advanced troubleshooting