# Windows – Do I need to enable UEFI to run Windows 10

biosuefiwindows 10

I have a Dell Precision Tower 5810 that came with Win7 (about 18 months ago, more specs at the bottom). After about 6 months, I formatted the disk and installed Win10 from an MSDN subscription. Didn't touch the BIOS. All was working fine until recently, when I started having problems that led me to the decision to reinstall.

I just found a CD that I got with the PC, which is the Win10 installation CD (which I had forgotten about when I installed from my USB). On the back is a big red sticker that says "Please ensure that the BIOS setting is set to UEFI mode prior to installing Windows 10. For more information please visit http://www.dell.com/support/article/uk/en/ukdhs1/SLN300634"

Now I never did that when I installed Win10 a year ago, and it all worked fine (until recently, but that was a different story).

Having seen articles claiming that if you don't have UEFI enabled, Windows won't support disks larger than 2Tb (which seems odd as I have a 6Tb external drive on my machine that I use for backups, and it's been working fine), I decided to enable it before reinstalling.

However, with UEFI enabled, I couldn't boot the machine, not from the installation CD and not from a bootable USB that I created with the Media Creation Tool. When I disabled it, I could boot, and have installed Windows 10 successfully.

So, do I need to have UEFI enabled? If so, can I enable it now, or would I have to reinstall? If I have to reinstall, how do I boot from the USB to install?

Thanks

Specs:
OS: Win 10 Pro 64-

• Manufacturer/Model Number: Dell Precision 5810
• OS: Win 10 Pro 64-bit
• CPU: Intel(R) Xeon(R) CPU E5-1630 v3 @ 3.70GHz
• Motherboard: Dell 0HHV7N (SOCKET 1) version A00
• Memory: 40Gb
• Graphics Card: 2 x AMD FirePro W4100
• Screen Resolution: 4 monitors, one at 2560×1440, three at 1920×1080
• Hard Drives: 1Tb Samsung SSD and 1Tb WD HDD. Usually have a 6Tb Seagate external drive plugged in for backups

Select your USB drive and Windows 10 ISO and make sure that the Partition Scheme is set as GPT partition scheme for UEFI and the File System is set as Fat32. You can then install Windows 10 in UEFI.