I messed up my Windows 7 and I need to run repair, but I don't have the CD. So, maybe it's possible to get just repair thing for free and mount it in USB and fix the Windows?
If the maker is Dell as indicated, they likely will offer a restore CD. That will restore the system to the condition it was when shipped. It will not be a Windows 7 disk that you can use for a repair. A call to support or use online chat for more info.
There will be a fee for the disk and shipping.
If your main concern is the data, you can possibly move the disk to another system in an external case or as a second drive and recover. You can also can use a bootable disk as noted by @Rob and recover in place.
That would let you do a recovery with a Dell recovery disk after the data is safe
Ask around to see if anyone you know has a Windows 7 install CD. As long as it's the same version that your CD key is for, it will work for a repair install (or fresh install). The back of your case should have a sticker with the CD key and version on it.