Boyfriend was downloading an app at weekend when iPod touch threw a wobbly and would not boot up. It was stuck on the apple logo and would not show up in iTunes. After much trawling through the net I found a fix for it:

Open itunes and then on your ipod shut it down but keep it plugged in.
After it shuts download hold the power button until you see the apple logo without releasing the power button hold down the home button until screen goes black
then without releasing the home button let go of sleep button and wait until you see your ipod in itunes then you can release home button

now click restore in itunes