The Windows 7 installer is running in UEFI mode. If you delete all the existing partitions, Windows should create a GPT partition scheme and install. Be aware that this will completely wipe all partitions on the disk including any recovery partition - no content previously on the disk will be accessible afterwards.
Alternatively you could run the installer in legacy mode (rather than UEFI mode) which will allow it to install to a disk with an MBR partition scheme. How you do it will vary, depending on your systems BIOS. On my PC for example, I press F12 when it first starts to get the "boot options" menu. Assuming I am using a Windows DVD I get the following choice (amongst others):
UEFI - TSSTcorp SH-S223C
TSSTcorp SH-S223C is just the make and model of my particular DVD drive
Choosing the one without "UEFI" in the name will cause it to boot from the DVD drive in legacy mode.
Ensure your BIOS is set to allow booting in legacy mode.
Edited by jonuk76, 30 June 2014 - 07:21 AM.