That OEM will appear if it's preinstalled at factory in which case it would have a COA sticker on teh PC, or a retail OEM System Builder license which is normally bought by those who build PC's to sell, or if it's been illegally cracked by a BIOS emulation piracy method. It would not appear with a retail copy of Windows 7.
There are two ways now to determine if its a legal Product Key:
Run the MGADiag.exe
, copy the results of it's report and post them back in the code box accessed by clicking on # in the toolbar in Reply box.
Call MS Customer Service to verify the Product Key against the Product ID.
At least you'll then know if you have a legal copy on board since if you Repair Install or Reinstall it will not reactivate using a bad Product key which has been used for cracktivation.
May I ask where you found the Product Key?