I just tried to install Linux mint on a SD card from a live system for a friend.
I managed to break his windows partition to the point that neither Mint nor the Windows recovery​ tool could read it and the SD card still won't boot.
I feel like a useless piece of shit and a bad friend.
At least his data is backed up but some of his licenses (Win, Office, ...) might be lost.

FIRST you need to minimize the Windows data to a Windows format (ntfs/fat32) and THEN to make the appropriate partition for Linux.

I learned that the hard way.....no backups

@lostinmyworld I don't want the Linux to run on the internal disk.
I want it to run from an SD card. (Where the files got successfully put. But somehow it still doesn't boot.)
However while working with the SD card the internal drive got modified as well. ( God damn side effects! )

Oh yeah I can relate. Don't feel bad though. Your friend knows that you were only trying to help. (Unless of course you were acting pro and all... Jk, 😋) for future reference my suggestion would be to get an external 1tb HDD and split it into two partitions, first being 8gb. Then get hirens boot dvd and transfer it in the first partition and make it bootable. Then before you do anything in case you are unsure, just pop it in and make a full clone of the drive (basically 2 clicks). If something goes wrong, roll back to the clone. This saved me around 6 months ago when I was in your exact situation.

The best part is your friend will not call you again to fix his computer/printer!

@cyberlord64 yeah, I got overeager.
I thought the entire thing would be done in an hour.
He gave me the stick with the live system because he didn't feel comfortable doing it alone.

Are you sure you didn't break only the bootloader?

@juzles well it doesn't get automounted in Mint and Windows recovery tools only recognise the drive but not the partition.
So no, not entirely but pretty sure.

I think sd cards and usb drives by default won't automount as you need them in the fstab config. And it's kind of dangerous setup if that device gets removed.

Sorry for being unclear. I was talking about the internal drive.