Removing freestlye xbox 360 chip/flash/mod?

Hi, I bought my son a second hand Xbox 360 slim. However, once we got it from the guy that sold it to us we discovered that it modded or chipped or something. The guy is now not answering his phone and we do not know his whereabouts as he delivered it to us. I'm so unhappy that he could do this. My son wants go on Xbox live to play Minecraft, Fifa. Etc. I'm not good with techy things, but how can get this off please.

Thank you

Added (1). So, does that that mean I can't get fixed? I'm happy to pay someone to get it back to normal so he can online with his friends.

If it is 'Blacklisted' then you will have to pay around £40 to get it unblacklisted. If the person has tried going online with a chipped Xbox (And has been found by Microsoft) they will have definitely Blacklisted the Xbox. I warn you, do not waste your time calling Microsoft Support. They will refuse to help you even if you didn't modify the Xbox yourself.

I suppose you have a RHG: "Reset Glitch Hacked" or "Jtaged xbox". You will not be able to get online because it's trying to spoof the xbox live servers and fails authentication but the pro's to having the Hacked system is you would not have to pay for games and it should come with pre-installed video games he should have a app called XeX menu and he can click on it and find a games folder then click on the game he wants to play then click the.xex file to run the game. The cons are you can't get online or you will risk bricking: Breaking the xbox or getting him banned from xboxlive I suggest you just buy a used xbox from gamestop.

Some Tutorials