Hello;
As luck would have it, I had this problem too.
My System: ASUS P4C800 with Maxtor 60+ gig drives and onboard cache. Windows XP, lots of ram (not relevant for this problem) and a generic power supply I got at Fry's outpost.
Anyway, for what its worth, here is my 2 cents..
Its not likely that IDE ports are going to be intermittently bad. I say this based on my experience. But to check it, I swapped IDE cables and ports just to be sure. No change in problem so I concluded my statement holds true.
Its also not likely the hard disk is bad since you are able to recover it by a simple reboot of the machine. If the HDD was bad or had a bad onboard chip then this problem would not be as simple as a re-powering on of the system (usually).
I have a Fluke meter which allows me to monitor voltages
on any part of the system using various wires & clips. I am sure the techs here know what Im talkin about. After a few days of monitoring, I was able to capture a drop in voltage across the power supply which I believe led to my system not "seeing" the hard drive. I repeated this with similar results by opening the power supply and tweaking settings. I dont recommend you do this unless you have training and/or some sort of engineering degree.
So if I were you, I would replace the power supply because it certainly sounds to me as if your having the same exact problem. Otherwise if you start replacing components without understanding their interaction/relationships, you could end up costing yourself a lot of time and money.
good luck, sorry for the long winded message...
Soldaten