This a common issue where customers are stuck between Dell and Microsoft and the Microsoft-OEM-customer triangle of blame. Dell Windows 7 Factory settings and Reinstallation DVDs use System Locked Preinstallation where a generic product key is automatically input and activation occurs if and only if a valid Dell BIOS is detected so Dell don't really care about the key on the COA. They have no logged entry of it and neither do Microsoft (who provided Dell with such low quality stickers causing the predicament you are in). There are a few cases where this activation goes wrong with such media and you are meant to be able to input your key from the COA and activate (which you can't). You will also get this problem if you try to clean install your OEM license using retail media such as installation media from Digital River. Assuming you have been reinstalling Windows 7 using a Digital River .iso, complete the installation by skipping the product key. You can then restore the Dell SLP product activation by use of the Activation Backup and Recovery Program and Dell files: [URL] For more details see A Clean install of Windows: [URL]
My hard drive died so I reinstalled my copy of windows 7 64bit home premium but I cannot seem to get it to register even though I am fairly certain of the code. (The laptop is over 3 years old and the sticker has rubbed off slightly) I talked to windows and they said that if it was an issue with the code then Dell would have a copy associated with my hardware since it came preinstalled. I talked to dell but they wouldnt talk to me because my warranty ran out long ago. I then talked to windows again and gave them control of my computer, they poked around and tried various things that I am afraid I didnt understand and then told me that Dell had somehow blocked my registration.  I dont understand how that could be but windows support told me that I needed dell to unblock me.  can anyone please help me understand what is going on? 
Windows is saying dell is somehow preventing me from registering my copy of 
windows after a reinstall