Convert GPT to MBR

I have got 3 Acer Laptops that came with Windows 7 & 8. We want them running Windows 7 so we can run TrueCrpyt. Truecrpt doesn’t work on drives that have a GUID Partition Table (GPT). So I found that I can do a DISKPART and remove all the partitions and convert to MBR. The drive shows has not being GPT. The bios is set to legacy boot. When I try installing Windows 7, I get “Windows cannot install to this disk. The selected disk has an MBR partition table. On EFI systems, Windows can only be installed to GPT disks.”

Anyone got any ideas on what I can do next?
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Nick RhodeIT DirectorCommented:
In the BIOS you can switch from EFI mode to BIOS mode.
Check the BIOS, disable EFI (or UEFI)
It could be that you have 3TB disks, you will lose the ability to have a partition larger than 2TB.
tetraukAuthor Commented:
The BIOS is set to Legacy BIOS and not UEFI.

The drive is only 500gb
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PowerEdgeTechIT ConsultantCommented:
Choose Repair Your Computer, then the Command Prompt option ... run diskpart:

select disk 0
convert mbr

The convert statement should fail as the 'clean' should revert GPT to MBR automatically.

Then try to install.
noxchoGlobal Support CoordinatorCommented:
Even if your BIOS says the drive is set in Legasy mode the EFI boot option seems to be set active. Disable it.
tetraukAuthor Commented:
In the end, I used a USB Pen drive to install windows (after I cleared all the partitions using DISKPART).

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Windows 7

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