So my nexus 7 finally got damaged. I bought a new screen and digitiser and with out hitch replaced the broken one with the new one . I thought all had gone well until i turned the nexus on after the new screen had been put in and an assortment of colored bars and boxes appeared. they do change every time i press the power button and when the screens change. It may be down to a software problem as i might have un plugged the battery by accident while the device was still on or the new screen could be defective.