IPhone 4 Verizon Help VIDEO Screen freezes and glitches? Diagnosis?

Hi, heres a video showing what it does exactly
I bought it online, and i don't know what the issue is. It seems to work fine by the sounds of it, its just the screen flashes, and goes to black eventually. The back light is still lit though. The phone wass recently flashed to Page Plus, on the same day i got it.

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