Soap, first check out what partition is mounted as the root partition:
Then, when you boot and end up in the login shell you were talking about, do:
[You'll get something like this:]
/dev/hdb5 on / type reiserfs (rw,noatime)
proc on /proc type proc (rw)
none on /dev type devfs (rw)
tmpfs on /mnt/.init.d type tmpfs (rw,mode=0644,size=2048k)
/dev/hdb6 on /home type reiserfs (rw,noatime)
tmpfs on /dev/shm type tmpfs (rw)
usbdevfs on /proc/bus/usb type usbdevfs (rw)
/dev/hdb8 on /mnt/storage type vfat (ro,gid=407,umask=027)
[Check the line which says '/dev/hdxx on / type foobar', the /dev/hdxxx is your root partition]
Make sure you use the right tool for filesystem checking. That is, for ext2/ext3 filesystems, it's e2fsck. For reiserfs, it's reiserfsck.
mount -o remount -o ro /
e2fsck /dev/hdxx (where /dev/hdxx is the device you got from the command above).