It seems to me that your hard disk is on the way out. I have noticed that the HD in my 7025 is operating at a much higher temperature than either those in my PC or
Sky Plus box. Much though I love my 7025, I do think it lacks adequate ventilation. What I think is happening is that your disk is OK cold, but slowly warms up and eventually overheats to the point where it stops working (even if it isn't working, the environment in which it is located is getting hotter and hotter)
My advice is to copy anything you want off the old disk before it's too late, and then install another, preferably outside of the DB using a molex extension and long IDE cable. That's certainly what I untend to do.
I also think the advice in the other thread may be relevant in that the DB power supply is operating at the limit of its available power and this won't help the hard disk.