Partitioning the drive won't do anything. And formatting the drive should be a last resort.
If it's a slave drive then wiping it clean really isn't a big deal...which is why I asked if it was the primary drive or not. Formatting would be the fastest, most simple and most reliable if it were indeed a slave drive and didn't have an OS on it. And the reason I said to do a partition too is because its always good practice to remap the drive before a format. The fact that he is having issues opening critical system utilities and folders would also lead to believe there might be an issue with the file system and a partition would definitely take care of that.