If there is an internal firewall then i don't know about it. I would imagine not, because i am able to see it from Explorer. And yes, there is plenty of room left on that hard drive (9+ G).
One thing that i tried and didn't work (and maybe this is a clue to the whole thing) is right clicking on that hard drive and then chosing to defrag it from the menue the pops up. The problem is that there is no such option for this drive, whereas it does exist for the drives that are in my laptop. I don't know why. Also, i tried running a defrag from the cmd prompt but again it wouldn't do it.