i have got a 320 gb external hard disk.it ws workin well.it was in good condition.suddenly i plugged it to my friend's computer,when i tried to open it,the computer showed me a message to format the hard disk.after that i tried to check the disk through the properties and also through tune up disk doctor,both the time it showed that "the disk is inaccesible".so what should i do it?is it because the files are damaged? pls suggest me a way....