Updated ubuntu on a dual boot system, and now it won't let me boot mint.

Hello, I've had a dual boot system for a year now and it's great, but I after updating the Ubuntu side via terminal, I could not see the mint boot from the grub startup menu. At first it was because it had rewritten the default time to 0, so I switched it to -1 and now I get the grub menu again, but the mint boot is no longer appearing.

When I look in the bios, it sees the drive, but if I put that drive as first priority it just gives me that line telling me to install a bootable drive.

I'm really hoping I don't have to reinstall mint, but if I do fine. But I'm wondering if anyone knows why my system can no longer boot from the mint drive if all i did was update ubuntu on the other drive.

Many thanks in advance!!