A well made Live_USB usb stick shouldn't install anything on your
harddisk, and there is no need to do so.
In this case it seems a grub boot loader was installed (which again
isn't something that should have happened).
The error message means the boot loader (used for booting Linux)
cannot find the "hard-disk" with Linux on it.
It is probably looking for the USB "drive".
Are you sure you get this message when you have removed the USB stick,
and have turned off the computer for some time? because its hard to
believe that a Live_USB stick should install a boot loader.
To remove the boot loader, (on your hard-disk) you should restore the
boot sector (the first sector on your hard-disk) with a windows boot
sector. There are many instructions on the web how to do it, as its
part of the normal uninstall of an installed Linux.
Normally its done with the Windows install disk.
Ask your friend to do it as he is responsible for your bad USB stick.