Do you have 250GB of free space on your internal drive?
If so, you could use ddrescue or dd_rescue to clone your external drive to an image file. Otherwise, if there are no bad sectors, you may be able to use your preferred cloning software instead.
Whether or not you have any free space, you could always examine your external drive in read-only mode. The first things to check are the partition table and boot sector. I suspect these are OK, but you could use Microsoft's Sector Inspector to confirm this.
http://www.users.on.net/~fzabkar/SecInspect.zipExtract the above archive to the one folder and execute the SIrun.bat file. The procedure will generate a report file named SIout.txt.