Secondary drives disappear & reappear when I reboot - on Windows XP

I have a PC running Windows XP SP2 with all patches updated.

Every so often one of more of my secondary drives just disappears.It

disappears suddenly while I am working on the PC.

At first I thought it was a problem with a Maxtor drive I have in my PC,

then I noticed that it also does it with a Seagate drive.

Now I am suspecting that it might be a Windows XP or hardware problem.

Help, any suggestions on how I can troubleshoot or any suggestions on what

could be causing this problem, what to do to fix it?

Thanks and Regards,

Ted M.