Can't buy songs in itunes store

itunes is up to date version on my PC. I've changed my ID and password having spent hours on apple chat support - to no avail. The problem: when i try to purchase a song in itunes a window opens asking for verification of Billing info. There are two options: verify Billing info or cancel. When i click verify Billing info nothing happens. No error message, no redirection, and most importantly - no purchase. Absolutely nothing. Any help resolving this problem?