Alaina , Since you have managed to hook up an external monitor and it is showing up, I would say the replacement monitor is faulty or the monitor cable could be loose or damage. One more thing you could try, would be is to delete the laptop monitor driver and reinstall, if no go then you may want to open up the computer and recheck the installation of monitor, check the cables and reseat the connections, after this retry and if still not working faulty monitor, return for replacement/refund. Good luck.
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