Intel motherboards often has BIOS that assumes Windows. Grub does not use a boot flag at all, Windows has to have a boot flag on a primary partition.
I think I was in a thread with srs5694 where we had to add a boot flag to a gpt partition even though that is not per the gpt rules.
I use BIOS to boot and have several drives partitioned to gpt. I now create an efi partition as I may get a new computer in the near future that uses UEFI and also have a bios_grub partition for grub with BIOS in gpt drives.
Post boot info script. The test version has some fixes:
Current version has some instructions if you need them:
wget -O bootinfoscript 'http://bootinfoscript.git.sourceforge.net/git/gitweb.cgi?p=bootinfoscript/bootinfoscript;a=blob_plain;f=bootinfoscript;hb=HEAD'
chmod a+x bootinfoscript
sudo bash bootinfoscript
Boot Info Script courtesy of forum members meierfra & Gert Hulselmans
Page with instructions and download:
Paste contents of results.txt in a New Reply, then highlight entire file and click on # in edit panel(code tags) to make it easier to read.
Or You can generate the tags first by pressing the # icon in the New Reply Edit toolbar and then paste the contents between the generated [ code] paste here [ /code] tags.
V60 has improved formating and requires code tags to make it legible. New Version is a zip file that you have to extract to get .sh to run.
Install these before running script:
sudo apt-get install gawk
sudo apt-get install xz-utils
Some simple things can be auto fixed with this and it runs the git/test version of boot script:
You can repair many boot issues with this or post the link to a run of boot info script so we can see your exact configuration.