Windows 10: System won't boot after converting main disk to GPT, unless I disconnect secondary disk...

Hello,I have a PC based on Gigabyte B550M DS3H, Rysen 5 3600, 16GB RAM.System disk is a 1Tb Samsung 970 Evo Plus SSD M.2 NVMe and there's also a 4Tb WD Red SATA for storage.Motherboard and SSD have latest firmware installed.OS was Windows 10 64-bit; I thought it was a good idea to upgrade to version 11 but my system didn't meet the requirements, as main disk was MBR and TPM/Secure boot were not enabled. So, I went on and: 1 converted main disk to GPT, using Microsoft's MBR2GPT tool, as described here: https://www.easeus.com/partition-manager-software/convert-mbr-to-gpt-gpt-to-mbr-using-cmd-wi

:)

 

Converting a MBR disk to a GPT disk

I would put Windows on Disk 2. There is plenty of space. If you want to start with a clean slate then you should do this:

• Disconnect disks 0 and 1.
• Boot the machine with your installation medium.
• Launch diskpart.
• Select disk 0 (it was disk 2 before).
• clean.
• Reboot with your installation medium.
• Install Windows.
• When it runs nicely, connect the other disks and tell the BIOS which is the primary disk to boot from.

Since disk 2 is only 232 GBytes you will not need UEFI / GPT. After Windows is installed you can convert the 3 TByte disk to GPT.

 

Converting a MBR disk to a GPT disk

When installing Windows I was asked which drive to install it on and selected the 3TB drive, whereupon it stated it couldn't install it on there as it had a MBR and needed a GPT drive.

-> OK, with such a large disk you must use the GPT partitioning scheme.

I then tried converting it to a GPT drive using diskpart etc through the Cmd prompt with Admin privileges. But when I got to selecting the disk it told me I couldn't select it because it had a Paging
File.

-> I am not surprised.

Went online to get MS Technician to help me and he said go into the BIOS, press Ctrl-Shift-Delete keys and then Diskpart etc to convert the disk to GPT.

-> What he probably said is that you need to set the "BIOS boot mode" to UEFI.

The Windows installation process gives you the option of partitioning and formatting your disk. It probably lets you choose the partitioning scheme too, MBR or GPT. I do not know for sure since I do not
have a disk > 2 TBytes that I could test. If not then you can do this:

• Boot the machine with your installation medium.
• Select Repair Mode, then the Command Prompt.
• Use diskpart.exe to partition & format the disk.
• Install Windows.

You might ask yourself if you really want a 3 TByte System Partition. I would go for a 100 GByte System partition and a 2.9 TByte data partition.

 

No boot disk found after converting disk to GPT

I have saved my data so I am fine with the data. When There are only 3 primary partitions and no other partitions I have converted MBR disk to GPT. Then went to BIOS and changed Legacy mode to UEFI mode. Thats when I observed UEFI mode didnot he any
boot options listed. Anyway I booted the notebook, as I was expecting, I got the error message. No bookable disk. Is there anyway we can get boot options to UEFI Mode? If not through cmd using the instal disk can we change the disk type from GPT toMBR without
losing windows. If not I just have to install windows afresh!!