There should be a C: somewhere. I think that one of the drives might be partitioned, so you have the C: and D: on the same disk. The other hard drive registered as H: should have other drives in between that made it go as H:. You should copy all your work from H: to the other drive then switch them both over so that the biggest drive is on the primary master. Then reformat and reinstall Windows on that drive. And make sure it's registered as C: first.