Dell Inspiron 5520 :: 8 Beeps But Display Started Showing White Lines At Top And Bottom

I have a 1 year old dell inspiron 5520 and about a month or two back, the display started showing white lines at the top and bottom. One day, it stopped working and we gave it to this tech guy. He replaced the motherboard and battery(The laptop worked but was noticeably slower). The white lines still existed and the screen started jumping up and down. Changing the refresh rate worked temporarily. And then my mother gave it to the tech guy again. She got suspicious of him and asked him to return it. And he did but now, the laptop display won't boot and there's the 8 beeps. I connected the laptop to our properly working PC monitor to see if it was the laptop's display's fault. But, it still gives 8 beeps and the monitor shows a blank black screen.