You've probably changed your BIOS setting to boot in UEFI mode only, removing the compatibility mode that allowed you to boot in BIOS mode. So now your system can boot in EFI mode and in that mode cannot use MBR partitions.
Note that you can convert MBR partitions to GPT partitions without loosing everything on that disk (Windows 10 allows that conversion).
But it's possible that you also reformated the disk with the wrong option.
Or may be you wanted to reinstall windows 10 after installeing windows 7 which partitioned it by default in MBR?
Try converting your disk with a tool like MiniTool Partition Wizard if your current version of Windows does not propose it in its Disk Manager.
And please specify which version of Windows you want to install... The storage requirements are not the same: upgrades are generally possible but downgrades not always supported without external management, or a complete repartitioning during setup (if you delete all partitions and select the empty disk, Windows setup should work and will choose a suitable partitioning scheme itself).
But before deleting and reinstalling everything, consider setting your BIOS to EFI boot mode, disable the "CSM" compatiblity mode (which could allow booting in legacy BIOS mode) and allow secure boot mode (should work now not just for Windows but for good Linux distribs as well). Make sure that your TPM module is also enabled, and that hardware virtualization are enabled. This has many advantages for the security (i.e. resistance to remote attacks and safer working mode for your security suite).
Then only, boot your USB key or DVD with that setting, and delete all partitions and reselect the disk (you don't necessarily need to partition the disk yourself, the Windows installer will make it for you in a suitable way and will install the proper EFI boot mode and the small recovery partition and will configure a clean BCD store in the small EFI partition).
Note that most Linux distribs still install the PC in legacy mode by default, you need to instruct them to use the EFI and secure boot mode manually in their installer.
After the installation you may resize one partition and the filesystem created in it to make space for an alternate OS, but I suggest you avoid the multiboot system and use a virtualizing hypervisor: this is often much more practical, and hypervisors are now very efficient; and virtualized OSes are easy to backup/repair/manage; and copy to give a try to some new software you want to test (with a strong isolation for your private data you son't necessarily want to share by default during the evaluation).
Virtualized OSes are also a very good way to create a very private store for your critical apps that you don't want to use in your default environment (e.g. to use with a minimalist browser to connect to your bank, or to protect some apps from children view for parental control, e.g. if you look at adult sites: it is possible to encrypt and secure your VM and not start it up automatically with your main OS and these apps and sites, frequently unsecure will also not have access to your other private data: I suggest using only Linux as the guest OS for using those sites, as it is safer than Windows and is simpler to manage/secure/update, with faster operations if you don't want to be forced to manage the VM immediately each time you use it, where Windows will constantly push notifications to make immediate updates, not just for security but in all apps).
If you want to have a virtualized Windows, I suggest you create a basic image and immediately update it and clean it up to the minimum, and then shut it down to create a safe backup that you can easily copy again on demand for tests. Sometimes you'll want to update or recreate this basic image from scratch: use the standard Windows downloader tool to use the latest released image for installing this VM, remove the undesired advertizing that are added by default and cleanup logs and restoration points once all is working, before shutting down, restarting it once without conencting, and then shut it down to create the backup of this new clean image. This preparation takes some time but with this backup it will be very fast to create a new VM for any new app you want to test temporarily before installing it in your main OS.
Thanks now Windows 10 has a good Hyper-V virtualizer builtin. But if your version of Windows does not have it, you can try with VirtualBox which supports multiple virtualized OSes and distributions. It is also a good way to evaluate various Linux distribs (note they take much less storage space than Windows).
Also your Seagate SATA HDD may have poor performance as a system disk, but will behave faster if it's used as a store for a virtualized OS image, because virtualized disks are also internally compressed and optimized (and so they have faster I/O accesses). You may also want to just convert this HDD to a storage volume for your photos/videos/music/documents, that don't require performance as they don't need very frequent random accesses. Consider using an SSD for the main system image, the paging files, registry hives and system user profiles and applications you use the most (and notably those prerunning at bootime with desktop extensions): a 128GB SSD is largely enough for Windows (even with heavy use and many apps), 64 GB works too but requires some regular cleanup, 32GB is really too small (too frequent need to cleanup, and lots of problems installing apps, caused by "C:" drive full) and may only be used as a secondary drive for the paging file and temp files.
Install your games library (e.g. Steam) on a secondary HDD, except your few favorite games as they frequently take considerable space.
the disk doesn't change configuration. It's that the legacy BIOS mode is turned off by you – phuclv – 2019-09-07T08:02:23.883
If EFI mode is enabled there is a good reason, likely due to the fact, your current installation was installed in that mode. Which means, if you disable it, you won't be able to boot to that installation. – Ramhound – 2019-09-07T08:59:15.023