Apparently the caps lock key works though.
I assume you mean "@" doesn't work, correct? Just the one key? If so, does the "2" key work (lower case "@")? If not, remove the key cap and see if there is anything preventing the key from traveling normally. If not, try a different keyboard and see if it works properly. If you have the same problem on a second keyboard, you can check to make sure "sticky keys" is not enabled. Other than that, I'm not sure what to say. As a stopgap, you can use the on-screen keyboard until you get the mechanical keyboard situation resolved.
As for D Drive, what IS D drive? Is it a partition or a separate HD? Data doesn't just disappear - how do you know the drive is empty?