Best answer by Nataly
Have you got SMETS1 meters?
These meters go 'dumb' when you switch suppliers which means the screens go blank until 'woken up' by pressing the keypad buttons - often the '9' or '6' (more info on the FAQ Marc linked to)
Hope that helps?
If pressing those buttons doesn't work, you can get in touch with our Member Services team via WattBot in your account and let them know your meter screens are blank. They'll then be able to let you know the next steps