ubuntu 16.10 won't boot, due to corrupt /dev/sda1

I have been successfully using 16.10 for some time now. The system doesn't now boot due to a corrupt /dev/sda1 file system. The screen error message is :-

/dev/sda1 contains a file system with errors,check forced.
Inodes that were part of a corrupted orphan linked list found.

/dev/sda1: UNEXPECTED INCONSISTENCY; RUN fsck MANUALLY.
(i.e., without -a or -p options)
fsck exited with status code 4
The root filesystem on dev/sda1 requires a manual fsck

Busybox v1.22.1 (Ubuntu 1:1.22.0-15ubuntu1) built-in shell (ash)
Enter 'help' for a list of built in commands.

(initramfs) _

Entering help brings up a long list of commands - non of which include RUN.

Any help would be much appreciated.