I am running ubuntu off a usb drive and accidentally unmounted my windows partition. Now my windows won't boot
That wouldn't do any damage.
Originally Posted by timothy9828
My guess would be you overwrote the Windows bootloader, or overwrote/deleted important files on the Windows partition.
If you have your Windows recovery CD/DVD you can quickly fix the bootloader problem. If some files were deleted or overwritten you may need to reinstall Windows.
In case you don't have your CDs, it may be possible to recover from a bootloader problem by installing a custom boorloader like EasyBCD or even GRUB,
Let us know how it goes.