I have samsung series 5 laptop.
I tried to downgrade to windows 7
Then by pressing F2 I disabled secure boot and set "CSM" as os mode
But I got error- "....The selected disk is of the GPT partition style." while selecting the partition.
Hence I deleted all the partition including oem reserved and recovery partition and continued the setup by selecting 1 of the 3 newly created drives.
Every thing was perfect but
SYSTEM IS NOT BOOTING
I get Samsung Logo and then cursor and again Samsung logo.....................This is continuous.
The bootloader is missing. Re-install windows and when you get to the point to choose a partition, click on the advanced option, delete the existing partitions and install to the unallocated space. This will create two partitions automatically, one bootloader and one for the win installation.