Unreadable COA labels turn out to be a common problem that Microsoft and the manufacturers have chosen to do nothing about. It's sh1t.
Worth trying this advice from a customer on the Dell website:
I have an alternative out of the box idea. I ran into this same problem with a totally unreadable Windows 7 COA. I noticed upon extemely close examination that the COA actually leaves very small indentations. If you take a very small amount of acrylic paint on your finger and very very lightly rub the area the numbers will start to reappear. It took about 30 – 45 minutes of tinkering and examining but now I can read all of my numbers. Only one number is within question. For clarity I could only read about 3 or 4 numbers / letters before this process. The numbers you see below were completely unreadable as was the words "Product Key". Hope this helps someone out. By the way my machine is totally dead right now without a hard drive so no software options will help me. I am sure there are others just like this.
Others report success doing this with ground-up pencil carbon and a gently applied pen.
My sticker was so badly worn that it looked like a blank white sticker. I tried this method: Basically I did the pencil thing, but because I didnt want to get too crazy, I just took a junk envelope and scribbled on it with the pencil for a bit until the envelope was saturated with graphite. I then rubbed the envelope portion that was covered in graphite onto the sticker.(Do not scribble directly onto the sticker!!) After a few minutes, I could start to see the bar code appear again, albeit extremely faded. Now, mine was so far gone that I didn't get the product key to appear nicely at all like the guy with the acrylics, but if I looked at it from just the right angle in the dawn light of my window, I could actually read it!!! It took several attempts to finally get it right and about 15 minutes of scribbling and rubbing. K and R, Q and O and 0, 5 and 6 were almost impossible to distinguish from one another, but before there was literally nothing there at all, even if I held it at any angle. So, I can tell you this WORKS, and it works so well I am astonished! I thought for sure my product key was gone for good…this is genius! Thanks so much!
Don't bother with the barcode – apparently it's a part number, not the product key.
Dave