I eventually upgraded to a newer motherboard with a new video card and memory and had no problems.
Recently I tried to build another PC using the old motherboard and it worked for a day or two then it wouldn't even come to post. I tried everything I could think of and what others suggested but couldn't get it to work at all. Arrrgh!
Then I noticed an article in a PC magazine about leaky capacitors. I went home, checked my mobo and there they were staring me in the face - 4 capacitors bulging and leaking brown stuff. I bought a new mobo and every part I thought might have been faulty worked beautifully.
Check this out for more info: http://www.tecnopoli.../leakycaps.html
I wonder how many mysterious problems reported in these forums may be caused by this.