How to change itunes store back to U.S. version on ipod touch?

i was checking out this ad for an app, and it brought me to the UK version of the itunes store on my ipod touch. now i can't buy anything off my ipod anymore because everything's in pounds and i'm not authorized in the UK store. i've tried syncing it to my computer mulitple times and changing the flag on my computer, but it doesn't help. i can't change anything about my account on my ipod anymore either, it won't let me select anything when i scroll to the bottom of the page. does anyone know how to fix this?