Updated to High Sierra overnight, main partition on the hard drive is now unusable.

I started the High Sierra update last night, and let it update overnight. When I woke up my computer was turned off, and when I started it up it said there was an error with the MPKG file. I opted to restart. When my computer restarted, it started in recovery mode.

My hard drive has two partitions: general storage and time machine. After the update, only the time machine partition is visible, and my primary partition has been renamed to "Unformatted". The unformatted partition is no longer accessible in Disk Utility, even though I can still see it as a partition.

Its inaccessibility is also preventing me from creating a time machine backup. It does not let me select this unformatted drive as a location to restore the backup. I am also incapable of resizing or removing the partition, as it is the first volume on the disk.

I am very worried that I lost all of the data in this partition, and I'm looking for guidance from the community to help me restore this lost partition and/or the data within it.