Problem with an error message concerning external hardrive

i have a 320 gb external harddrive u know to take some wieght of my considerably smaller sized computer hard (i think 120gb) and an error message comes up saying

"F:M$ft The data has been lost. This error may be caused by a failure of your company hardware or network connection. Please try to save this file elsewhere.)"

it started coming up heaps on all different folders and files (i think files at least) on my External Harddive then i noticed that with the data had been lost and all that it may be deleting all my files so on instinct i quickly switched of my external harddrive and the message hasn't come on since. another strage thing is when i pluged in my PSP it also said the above and when i tried to navigate through my PSP the files just weren't there just blank like there was nothing on it. Can anyone please help me with this problem?
and how to fix it permantly with
a) without potensialy damaging my computer
b) without removing any components within the computer
c) without making any extreme changes to my computer without making either slow or considerably very different
if push comes to shove then yes i will move to more drastic measures