Computer can't find startup system, command+R and others not working

Hi,

I bought this macbook off amazon a few days ago. It worked great for two days, then I left it plugged in overnight and when I tried to turn it on in the morning it showed me a black screen with a flashing folder icon with a question mark in it. I've tried many restarts since then but it has never showed me that icon again. Also, that morning the bottom of the computer was somewhat warm.

When I turn on the computer normally, the screen turns on but it is just a lighter shade of black. Even if it is left on for an hour, the screen never changes. The startup chime does play and it sounds the same as if it was a normal startup. The fans do not turn on.

I tried every combination of keys from this website except for N. The only key combination that does anything is Option-Command (⌘)-P-R. This makes the screen briefly flash, then play the startup chime twice as it should. Regardless of whether I stop pressing the keys after the second chime, the startup is the same as before. I've also tried every combination of startup keys after the second chime but it does not change anything.

I have tried holding Command-R and Option-Command-R for up to fifteen minutes but nothing happens. The other combinations I tried holding for at most five minutes. Again, with the exception of Option-Command (⌘)-P-R, no key combination changes the startup behavior.

I tried the combinations while it was plugged in, then left the screen on and let the battery drain. Once it was drained, I left it for another day then plugged it in and tried again. Nothing changed. There was 120GB of storage left on the disk before it died.

I am a student without a car so I can't realistically go to an Apple store. The on-campus tech store charges $75/hr so I don't really want to go there. Is there anything I can do, or should I just send it back?