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Hello and thank you for your question, I look forward to assisting you today. What make and model of computer are you using please?
Okay, thank you. This is most likely caused by Windows 10 and not a virus. First thing is to make sure you have a backup of your important data before go any farther. My next question is, do you have a Windows 7 installation CD, and how old is your computer?
There should be a system restore DVD that came with your computer. Do you have anything marked as such?
There are a couple of ways to do this. Can you boor into Windows 10 without any issues?
If you would like to try Windows 10 again, you might find you'll will like it once it is installed and working. If you would like to, go to this LINK. There you can download Windows 10. Once you do that you will need to burn it to a DVD. What you will download is what is called an iso file. You will need a specific program to burn the Windows file to your DVD. You can download that at this LINK. After Windows 10 is burned to the DVD, you will then use that disc to boot your computer from. Follow the on screen instructions for installation. Let me know if you run into problems. If you still would prefer Windows 7 you can reinstall it the same way. I'm available to assist regardless of what you dercide.
My thinking now is, with the importance of the files you are trying to save, maybe you should consider purchasing a new hard drive and removing this one and using it for backup and storage? Drives are pretty cheap and you probably wouldn't go through as much hassle installing a new drive. If you want to go that route, let me know and we can proceed from there.
Your Windows 7 key should work just fine. If not, I will give you instructions to contact Microsoft and they will give you a new key. As long as you have a legitimate copy of Windows 7 running, the Windows 10 upgrade is free.
You should have a Microsoft sticker on your computer with the activation key on it. Check for that, and that should get you up and going. You should be able to install Windows 7 as a new install. That would partition and format the drive and remove any old files left behind by Ubuntu.
About your only option then other than buying a retail Windows 7 key, is to contact Microsoft Support. If you registered your Windows 7, they should be able to provide you with a replacement key. If you can't get a replacement from MS, I may be able to provide you with access to purchase a key. I have done that in the past and it was very reasonable.