Do I need to convert MBR to GPT to do a clean install?

Hi,

I have some tech knowledge, but not an expert! I can disassemble/remove parts from my laptop with proper instruction, etc. I have an odd situation. I have an Alienware17 that I currently cannot boot. It originally came with Win7Pro, then I did the free Win10 upgrade. After a few months one of the auto updates failed over and over again. Every time it failed, it tried the next day and I got tired of the daily loop of reboots and failures. So I attempted to recover Win7, which was difficult (for me anyway) and time consuming as it was past the timeframe to do it from within Win10. In the end I was successful and have been back on 7 for several months. In any case, last night, my system suddenly crashes (as I was putting it into hibernate) with a BSOD. The next morning, I go to start up and get it again, UMOUNTABLE_BOOT_VOLUME, and then a message saying Missing Operating System. I read up on the various causes, removed the HD and attached it to my older laptop to run virus scans, etc, and it all checked out fine. I considered trying to repair the MBR, but I couldn't even get to a command prompt. Since repairing the MBR was a little over my head, I figured maybe it was time to attempt a clean install of 10 again.

The previous versions were running in Legacy mode. I created the Win10 installation media for USB, but when trying to change the boot order, USB wasn't even listed in Legacy. Changing it to UEFI allowed USB to appear. So now I go to install and it is showing 4 partitions. (I tried attaching a picture I took from my phone, but it seems to not be working?) So I have:

Drive 0 Partition 1 Total Size: 39 MB Free Space: 39 MB (OEM Reserved)
Drive 0 Partition 2 Total Size: 10.2 GB Free Space 10.2 GB Primary
Drive 0 Partition 3 Total Space: 921.3 GB Free Space: 921.3 GB System
Drive 1 Partition 1: DATAPART1 Total Space: 10.5 Free Space: 10.4 GB Primary (This is my SSD)

No matter which I select, it says that Windows can't be installed to this disk because it has an MBR partition table. I understand this MBR is for Legacy boot and the GPT is for the UEFI boot. So I guess I just need to know how to proceed. Do I delete a partition(s)? Format? Since I can't currently boot from USB in Legacy, I figure I need to convert these to GPT. Since I didn't solve the problem described in the BSOD, I figure the reserved partition is useless now. (I had already tried running repair through BIOS, booting to safe mode, etc...nothing worked.)

Am I supposed to install to the SSD? (and why is that the only partition where total space and free space are slightly different?) My only selections available are Refresh, Delete, Format, or Load Driver. Afraid to do anything I can't recover from, although I seem to be at ground zero anyway, right? Appreciate any help!

Drive 1 Partition 1: DATAPART1 Total Space: 10.5 Free Space: 10.4 GB Primary (This is my SSD)

If desiring to use the SSD, I see that as a problem, Total Space of 10.5 is insufficient to install Windows. I haven't seen anything smaller than 32GB on some Notebooks and most Tablets. Based on the figures given there is nothing useful on any of the drives/partitions.

Personally I prefer to wipe all partitions from drives [bootable GPARTED CD], disconnect those not necessary for the install then boot to the media, either USB or DVD and do the full install on Drive/Disk 0 as defined by where plugged into on the motherboard and detected by the BIOS.

I was unable to boot from USB using Legacy, hence my issue.

From what I read, it seemed UEFI was better anyway?

@BellFreak,

Windows 10 will install with the type of partitioning required for the method the installer was booted with. Boot the installer in legacy BIOS (CSM) mode and it will install onto the hard drive or SSD with MBR partitioning and a partition marked as Active with the boot files. Boot the installer in UEFI mode and it will install onto the hard drive or SSD with GPT partitioning and a FAT32 EFI System Partition with the boot files.

First - how did you create the Windows 10 installation USB flash drive? If you use the Microsoft Media Creation Tool and just let it create the flash drive for you, the flash drive will be bootable on both legacy BIOS and UEFI systems.
Download Windows 10

If you have the Windows 10 ISO file saved, it's easy to make a USB flash drive bootable in Windows without any extra third party programs.

Insert the flash drive
Open a Command Prompt (Admin) or Powershell (Admin) or "Run As Administrator" Command Prompt. Then run the following commands in the window:

diskpart
list disk
select disk # <-replace # with the actual number of the USB flash drive
clean <- this will erase the disk selected above, make sure it is the USB flash drive!
create part pri
format fs=fat32 quick
active
assign
exit
exit

Then mount the saved Windows 10 ISO file. In Windows 8 or 10 you should be able to just right click on the ISO file and select mount. For Windows 7 you need a program such as WinCDEmu:
WinCDEmu - the easiest way to mount an ISO. And more...

Once you have the ISO file mounted, just copy all the files and folders from the mounted ISO file to the USB flash drive. That's all you have to do, the flash drive will be bootable in both legacy BIOS and UEFI modes. If you used RUFUS to make the flash drive what you get will depend on the settings you selected and even in what order you set the settings. I do not recommend using RUFUS. The two methods above are much easier to create the flash drive with and you get a flash drive bootable in both legacy BIOS and UEFI.

Once you boot the USB flash drive, select the Custom Install option when you get the choice. On the next screen you will want to delete each partition on Drive 0. When you have nothing but unallocated space left on Drive 0, highlight the unallocated space and click next. Windows setup will set up the hard drive for you and install Windows. Then as long as you boot from the hard drive in the same mode (legacy BIOS or UEFI) that you booted the USB flash drive from, you should be good to go.