Linux booting problem

My PC (P4 3 GHz) has both Windows XP and Linux (Knoppix) installed. Recently, during the booting of Linux, the following messages were issued:

Checking root file system ...
WARNING: Your /etc/fstab does not contain the fsck passno field. I will kludge around things for you, but you should fix your /etc/fstab file as soon as you can.

fsck.ext2: Is a directory while trying to open //:
The superblock could not be read or does not describe a correct ext2 file system. If the device is valid and it really contains an ext2 filesystem (and not swap or ufs or something else), then the superblock is corrupt, and you might try running e2fsck with an alternate superblock:
e2fsck -b 8193 <device>

fsck failed. Please repair mannualy and reboot. Please note that the root file system is currently mounted read-only. To remount it read-write:
# mount -n -o remount, rw /

Could somebody help me to solve this problem? :cry: Thanks.