KT400 - Drives disappear

Seem to have a problem that is getting worse as time goes on, but
something I have never experienced before. First it started with the 2nd
CD drive I had just disconnecting at random. Eventually I unplugged this
to just have the DVD+RW on the second IDE channel. After some time the
lone DVD drive would just suddenly disappear from the system. Now, I
find one of the hard drives doing the same. When I reset or reboot the
computer the drives are not seen. Put if I completely power off and
restart they are seen again and everything works fine.

I suspect it may have something to do with the power supply, but
recently I swapped power units and it is still doing the same. Is this
possibly a know issue with these boards?