Cannot boot into Windows after creating a new partition

Remove Windows and reinstall your MacOS. Then start over with Boot Camp and create a partition the size you need/want.

You can not create a partition on a drive already containing a Boot Camp partition.

1. Once you corrupted the drive by trying to create another partition, you likely can not remove Windows using Boot Camp Assistant. You will have to format your drive.
2. Hopefully you kept good backups before you created the additional partition. If not, you will lose all your data on the Windows partition. Before proceeding to reformat your drive, make sure you create/have a backup of your Mac partiton data.
3. When you format your drive you will lose all partitions and data on the drive.

Boot into macOS and retrieve the files from the Windows partition. macOS has the ability to read an NTFS volume (macOS cannot write to an NTFS volume). Also make sure you have a good backup of the data on your macOS volume as well.

Then try deleting the new "U" partition to try to merge it back into the macOS Container. I have no idea if this will work, but what do you have to lose if you have your data backed up. Then see if you can boot into Windows. I think the main problem is the Windows bootloader uses a partition number to locate where the Windows system files are located and you introduced another partition which throws this count off. Sometimes on a standard PC it may be possible to run the Windows installer to attempt to repair the bootloader links or to manually edit the Windows' boot configuration files, but I have no idea if it would work on a Mac with BootCamp (it is even difficult on a regular PC). While I've done this years ago on a standard PC, the last time I attempted it, I gave up since it is hard to find the necessary information online since most instructions are dealing with a very basic configuration. Windows' documentation is just as lacking as Apple's.

You could try running BootCamp Assistant to remove Windows, but I don't know if it is possible to merge that space back into the "U" partition. I doubt it, but it doesn't hurt to try.

Your only other option is to erase the whole physical drive, followed by reinstalling macOS and restoring from a backup. Then use BootCamp Assistant to reinstall Windows. I highly recommend you create a bootable macOS USB installer while you still have access to macOS. While you should be able to reinstall macOS from Recovery Mode (Command + R), or Internet Recovery Mode (Command + Option + R), sometimes people have issues problems due to network or ISP issues. Better to be over prepared with several options and not need everything. Within Disk Utility you may need to click "View" and select "Show All Devices" before the physical drive ("Apple HDD HT5410....") appears on the left pane of Disk Utility. If installing macOS 10.14+, erase the physical drive as GUID partition and APFS (top option), otherwise for older versions of macOS erase the physical drive as GUID partition and MacOS Extended (Journaled).

The one forum contributor who was a master at dealing with partition issues has not posted on here in a long time. As you have seen from those other posts there was basically one contributor who was helping the majority of users with partition issues.

You should always have frequent and regular backups of your computer(s) and all external media (including the cloud) which contains important & unique data. For users with Windows BootCamp, make sure to back up Windows as well.

NTFS is the format of the Boot Camp partition. You may be able to access the data on the Boot Camp partition when booted into MacOS. If you can access these files you can copy them to your Mac partition or to an external drive.

If for some reason you cannot boot macOS, or macOS is unable to access the Windows' partition, then depending on the model of the Mac (older non-USB-C Macs), you may be able to create a bootable Knoppix Linux USB stick which generally will be able to access data on just about any non-encrypted partition. You will need another spare drive or network share to temporarily store any recovered files. I'm actually not sure of the best choice of file system to use on the destination drive since I normally have my own custom setups. I believe Knoppix can write to an NTFS volume, possibly exFAT, possibly an HFS/HFS+ volume as long as Journaling is disabled although this may require installing the HFS/HFS+ software first. FAT32 is not usually a good choice due to file size limitations and drive size limitations among other things. SMB network shares are fine too.

If macOS won't boot to the internal drive, then another option would be to install macOS to an external USB3 drive and boot from the external drive.

So there are options. At least one of these is likely to be able to access the Windows partition as long as that partition has not been damaged. In that case data recovery software would be needed.

Good luck.

3Dwayne3 wrote:

I believe I see all my files from my Windows partition now. I'll attempt to copy them to my Mac partition since I don't have an external drive sufficient enough to hold all the data. I'll be back once I've done this.

Once you recover those files, don't do anything else to this drive until you have a backup of these recovered files and also of your macOS files stored on external media (do not use a USB stick for the only copy). Modifying partitions is always risky so you don't want the only copy of your data on the drive you are modifying.