External HD unaccessible

i have a 250GB external USB/Firewire drive. when i turned it on today, and double-clicked the icon, i got the error message:

M:/ is not accessible. the file or directory is corrupted and unreadable.

i was able to use this drive the other day. i have tried it on my other computer which resulted in the same error message.

i checked the properties, and oddly enough, instead of NTFS, it shows RAW.

any help would be appreciated.