All over the screen or just part of it? Remove all cables from it and see if the menu has corruption on it or not when not connected to the PC after a few minutes of being switched off. First port of call is to change the cable for a different one. If that doesn't fix it and your old monitor still works, its either the monitor itself being faulty (most likely) or if the GPU output is different (say you are using DP instead of DVI this time), it could be the GPU instead.