Hi, I have a Dell PC which I had bought in 2012 and it came with Windows 7 Home. Then when Windows 8 came, I had upgraded the 7 to 8. Now I downloaded the Windows 10 ISO from Microsoft tool and booted the PC from the DVD. It asked for key and when I entered the key which is listed on my Dell CPU, but it said, invalid. Then I skipped it and went ahead with installer, formatted the OS drive. Now the windows 10 is installed and its now asking for me the key. I entered the same windows 7 key which I have but it says invalid. Now what to do ? And I see the graphics shows bad. Do I need to install the graphics driver again ?