If it's really an untouched 360 then the Laser could just need cleaned, adjusting or worst case replaced. If it's an unmodded, unopened and untouched 360 you aren't going to have to mess with any FW or drive replacing, just the laser at most.
You're going to have to tear the thing apart to clean, adjust or replace the laser, so start looking for a tutorial on just that, plenty around on how to get the 360 apart. Then there's either gonna be 4 or 6 screws, depending on the drive that's in it, to get the cover removed from the DVD drive. Then you can try cleaning the lens of the laser first, put it back together and test, then try the POT tweak (tutorial here
Now if after a good cleaning and the POT tweak it doesn't read any XBOX or 360 games, try as many as ya can to see if even 1 will boot, then depending on that outcome you have 2 options.
1. It boots at least 1 game, so ya know the drives key is good and the the laser is really screwy and a new one should fix it right up.
2. It still reads no games, you get a new laser and install it and it still reads no games, that means ya got lied to and the drives key is messed up and the thing is really useless, unless the owner has the original FW or key backed up somewhere.