My iPhone takes hours to turn on and the screen has looks vignette

i recently smashed my iphone really bad and then got it fixed and it seemed fine now it takes hours to turn back on and the screen has all these little vertical grey lines and for some reason the whole screen has a weird vignette effect what could this be or how can i fix this ?also when i open apps and then go back on the home screen and open a different app and i can see the app that i was previously on faintly in the background .