Just had the same problem, which was specifically thanks to Dell DataSafe. First encountered the problem when Dell DataSafe did an update and restart and then Grub bailed at a very early stage leaving me with no interaction with the system at all.
After the panic subdued, and many hours googling, a restoration of Grub solved the problem. First thing I did after that was to log in to Windows 7 and uninstall Dell DataSafe - which of course, borked my MBR again! Doh! Thankfully, its a painless process to restore the mbr once I knew what I was doing.
Always read the more detailed topics for thorough advice, but Ill outline the solution that worked for me in case it helps others:
1. Boot up from live CD.
2. Open terminal.
3. Mount linux partition - sudo mkdir /mnt/mint; sudo mount /dev/sdb1 /mnt/mint (Needed in order for grub-install to work).
4. Restore grub to the mbr: sudo grub-install --root-directory=/mnt/mint /dev/sda
This installed a fresh copy of grub into the mbr but did not seem to pick up the correct configuration - on reboot, I at least managed to get to a grub> prompt rather than it just aborting, but there was no dual boot menu. Some research on manual booting taught me the following for booting from grub:
4.9 If you do not know which partition grub/kernel is installed on, use "find /boot/grub/stage1" to let grub locate it for you. This should return a partition locator in the form, (hdx, y). Use this value in the following commands.
5. root (hd1, 0)
6. "kernel (hd1, 0)/vmlinuz ro root=/dev/sdb1" - vmlinuz<tab> will autocomplete.
7. "initrd (hd1, 0)/initrd" - initrd<tab> will autocomplete.
This booted my Linux Mint install... and helped me relax a bit.
The last steps I had to do were:
9. Once booted, open a terminal.
10. sudo update-grub2 - this regenerates the grub config data. This might not be needed, but I definitely did it so Im not sure if its essential. Its likely the previous config was still OK I think.
11. Restore grub to the mbr again with sudo grub-install /dev/sda - since we are booted/running from the correct install, there is no need for --root-directory.
After this, my system was restored. Im sure there might be some steps that arent quite essential, and probably a slightly more efficient solution, but it worked for me.