I installed it but all my files have been lost. I had Windows 7 before that.
How do I remove Ubuntu from my computer? How do I recover my files?
Have you overwritten your Win7 volume with Ubuntu installation?
Please don't try removing Ubuntu first, instead, recover your data before writing anything to your hard disk, as early as you can. Try boot WinPE from your USB disk, and run data recovery tools like Easy Recovery, FinalData, Recuva, etc. (Please be patient while your data are recovered, while running any of those tools or others.)
After that you just need to reinstall Win7 on that partition. If you can't boot from your new Win7 on you hard disk, you should repair your MBR, perhaps this blog can help you.
Best luck with you!
sudo fdisk -l
it will ask for your password, edit your question and add the result. We will have an idea of what happened to your files if you do so.