Normally with Acronis True Image you would create an *IMAGE* (a .TIB file) of your C drive in the external drive. You can then boot with the Acronis CD (or Recovery Media you created) and restore that image to your PC's hard drive.
If you've actually "cloned" your PC's hard drive, can you boot with Acronis Recovery Media and then "clone" the external hard drive back to the PC's hard drive?
Let's hope that works but, in future, you should create a backup image of your hard drive instead of cloning it. A hard drive is normally cloned either because you suspect it is in imminent danger of failing or because you want to replace it with a larger drive. Also, by creating an image file in the external drive, the drive can still be used for storing other files.