I read all of the forum rules, so I hope I am not breaking them. I have a computer called "HP Pavilion a620n". It came with Windows XP. The Windows installation broke a long time ago (it won't boot and the drive shows warnings of imminent failure), so I've been using Linux for the past four years on a different hard drive. I would like to install Windows XP again just to play my old games. At the time of purchase, this computer came with the first service pack, but I don't know if it was using "SP1" or "SP1a". The only difference with SP1a is that Microsoft removed Java from the installation. I downloaded ISO files of both SP1 and SP1a with SHA1 codes that match the ones listed in this forum. I've read that the Product Keys for Windows XP will only work on the actual Service Pack version that a computer originally came with, so trying to install an ISO of Windows with SP2 would say my Product Key is invalid since it was designed to be used with SP1. But does it also matter whether I use an SP1 or SP1a ISO? The difference between SP1 and SP1a is so small, and I cannot find a way to check if the computer had SP1 or SP1a at the time of purchase. Can I just use either one? I checked the Windows Registry within Linux and it says this number for my Product ID: "55277-OEM" Another website says the number "55277" means it's a generic OEM installation, so I downloaded ISOs of Windows XP SP1 and SP1a with the same ID of "55277-OEM". The company put a sticker on my desktop with a Product Key, but I read it's better to use the Product Key within the Windows Registry. I only have access to Linux, so I tried a lot of different Registry Viewers with the help of the Wine Emulator. I only found one Registry Viewer that actually works within Wine. I used the Registry Viewer to find something called "DigitalProductID". I would like to know if it's different than the Product Key placed on the sticker on my desktop. The DigitalProductID is encrypted. I found a website that has a decrypter, but I'm not allowed to post links. The website shows instructions for how to find which numbers to type into their decrypter. Their instructions say I should find 15 sets of numbers within the encrypted code, but they show an example that doesn't make sense. This is what the website says: Code: Double-click on DigitalProductID. This is the entry that contains the encoded product key. We want the information in bytes 52 to 66. You can use the chart below for reference. We need the 15 sets of numbers where the 1’s are located. 0000 00 00 00 00 00 00 00 00 .. 0008 00 00 00 00 00 00 00 00 .. 0010 00 00 00 00 00 00 00 00 .. 0018 00 00 00 00 00 00 00 00 .. 0020 00 00 00 00 00 00 00 00 .. 0028 00 00 00 00 00 00 00 00 .. 0030 00 00 00 00 11 11 11 11 .. 0038 11 11 11 11 11 11 11 11 .. 0040 11 11 11 00 00 00 00 00 .. 0048 00 00 00 00 00 00 00 00 .. 0050 00 00 00 00 00 00 00 00 .. But the code I see within my Registry Viewer doesn't look like that. Their chart shows numbers arranged in 9 sets horizontally and 11 vertically, but the numbers I see in my registry are not arranged like that. And their chart has a total of 120 digits, while the code in my registry has 328 digits. And even if I could understand what they're talking about, I would still be afraid to get it decrypted with their website because they could just be storing my Product Key and using it for themselves. So what should I do? Do you know of a way to decrypt the DigitalProductID, or should I just use the Product Key written on the sticker? I've heard that the code from the sticker might require a call to Microsoft in order to get activated, but Microsoft would deny my request since they no longer support Windows XP. The Product Key within the DigitalProductID is supposed to work instantly. So what else am I missing? Is there anything else left to do before I can install Windows XP? If I finally get access to the Key, will the ISO I have instantly work? Since HP used an ISO called "55277-OEM", does that mean the same ISO I downloaded will work without any modifications necessary? I'm afraid to try without knowing everything first because I'm afraid I might mess something up. Please tell me what other steps are left. I hope I'm not breaking the forum's rules with this message. This seems legal since I am trying to get my own Product Key that I actually own. Thanks for any help.