A Dell Windows 7 Professional 64 Bit Reinstallation DVD will apply Dell OEM SLP activation which will activate when installed on your OptiPlex 990 via BIOS.
I have a used Dell Optiplex 990. It came with a 32 bit version of Win 7 installed. I need to reinstall Win 7 with a new hard drive. I've added RAM (12 GB). If I install Windows using a Dell Win 7 Pro restore disc, will my existing Windows key activate it?  Thank you.
Reinstall Win 7 Pro: change 32 bit to 64 bit?