I presume you've turned it off and on in the past three months. That's always the first thing I try when tech is giving me trouble. With laptops, if that doesn't work, I then try turning it off and then taking the battery out. Leave the battery out for a minute and then put it back in and try again. If that doesn't work then I would see what the stores return policy is.
I'm on mobile but I would also try searching the problem online if you haven't already
If anything, I would just tell you to return or RMA it. But if you're feeling daring you can check to see if the cable for the monitor has come loose. But that might void any warranties and if you're not experienced enough you can end up causing more harm to the laptop. Also, it might not even solve the problem. It sounds more like there are some problems with power going into the GPU. So replacing the battery or taking it out and putting it back in like dripandrip said might work too.