If you are in the US fill out the request for disks here:
If you are not in US, contact Support in your country.
Please share the system's Service Tag and and Owner's Name with me via private message (click my username and then click Start Conversation). I will review the account information and share the further course of action with you. Please reply with the information, I'll be happy to assist further.
See Windows Reinstallation Guide/A Clean Install of Windows 7:
Use media from Digital River if you cannot procure it from Dell.