I have 4 hard disks (I am on Debian LiveCD now):
user@debian:~$ sudo blkid /dev/sda1: LABEL="System Reserved" UUID="EE2CE1122CE0D71D" TYPE="ntfs" /dev/sda2: UUID="AEB0F4D6B0F4A64D" TYPE="ntfs" /dev/sda3: LABEL="WINYANCI" UUID="40BCF0AABCF09B9A" TYPE="ntfs" /dev/sdb5: LABEL="YAHSI" UUID="8efb4a53-f0fd-4e24-8217-1f27dff3d2b5" TYPE="ext4" /dev/sdc2: UUID="5c65c579-a385-4d89-b979-04c2c182d040" TYPE="swap" /dev/sdc3: UUID="c9a6ef89-c1b6-4827-8e3c-2ec39fcb1265" TYPE="ext4" /dev/sdc4: UUID="110b5c0c-cd0e-4284-99a5-61fe02c217ec" TYPE="ext4" /dev/sdc5: UUID="6ec4938a-71a7-4ea1-a9e6-9ed0c90c4a45" TYPE="ext4" /dev/sdc6: UUID="5D641D223A2A64B4" TYPE="ntfs" /dev/sdd2: LABEL="DEPO" UUID="02D8A6A9D8A69A85" TYPE="ntfs" /dev/sdd5: LABEL="HUSUSI" UUID="E0949947949920D8" TYPE="ntfs" /dev/sr0: LABEL="Debian wheezy 20140209-18:05" TYPE="iso9660" /dev/loop0: TYPE="squashfs" sdc is the new 1 TB hard disk, sda is where I have Windows 7 installed (and the old GRUB in MBR from my previous Debian installation) and sdb and sdd are just storage. Since I've bought a new shiny disk and I wanted to use GPT on my new disk and then partitioned it like this:
user@debian:~$ sudo gdisk /dev/sdc GPT fdisk (gdisk) version 0.8.5 Partition table scan: MBR: protective BSD: not present APM: not present GPT: present Found valid GPT with protective MBR; using GPT. Command (? for help): p Disk /dev/sdc: 1953525168 sectors, 931.5 GiB Logical sector size: 512 bytes Disk identifier (GUID): 2758BB06-C7E7-451B-9C92-F1B278721BB6 Partition table holds up to 128 entries First usable sector is 34, last usable sector is 1953525134 Partitions will be aligned on 2048-sector boundaries Total free space is 3437 sectors (1.7 MiB) Number Start (sector) End (sector) Size Code Name 1 2048 6143 2.0 MiB EF02 2 6144 8394751 4.0 GiB 8200 3 8394752 76754943 32.6 GiB EF00 4 76754944 174409727 46.6 GiB 0700 5 174409728 1346283519 558.8 GiB 0700 6 1346283520 1953523711 289.6 GiB 0700 Then I went on to install Debian on sdc3 (which is /, sdc4 is /home). Installer asked me if it should install GRUB on MBR of sda. I said 'no' because there is a 2 MiB partition with grub_bios flag on sdc (since my old motherboard doesn't have UEFI) and I wanted to install GRUB there: 
Now, GRUB won't boot! Either it conflicts with the 'old' GRUB in sda's MBR (I thought, when I said GRUB to install on sdc there would be only one GRUB on sdc's GPT) or I failed to install GRUB correctly or installing it on sdc5 was completely stupid while I should have installed it on sdc1 or somewhere else on sdc... Any ideas how to solve this? 
PS: I have tried to reinstall GRUB reading this tutorial but again the same error (this time I chose /dev/sdc as the location to install GRUB).