Things You'll Need
Instructions
Go to Xbox's Service Center (see "References") website and click start repair request. Fill in your information and get a shipping shipping address and repair request number.
Call Microsoft Xbox's support at 800-4MY-XBOX (800-469-9269) and let them know you have just purchased a modded Xbox and would like to have the original software reinstalled onto the system. Give the agent your repair request number so he can put this into your file. He will likely ask for a copy of the receipt to prove you have recently purchased the system and haven't tried modding it yourself.
Package just the Xbox system. None of the accessories, wires or power cords should be sent. Place the copied receipt and the repair request number into an envelope and stick it inside the box. Encase the system with styrofoam peanuts, bubble wrap or simple newspaper so the system doesn't get damaged during shipping.
Send to Microsoft via USPS, UPS or FedEx. Check the status of your repair on Xbox's Service Center by entering your request number and postal code.