Memory problem?

Hi Folks. Just wanted to say thanks as your expertise here has helped me solve more than a couple computer issues. Now that I have joined I will try and contribute and help some members as well.
With that out of the way I do have a problem that I just cant figure out. I had to reformat my computer and rebuild OS and software. When I was done my computer now only starts half the time. If you turn it on it will wait a couple of secs and then gives off long bios beeps that keeps repeating. It is the same long beep over and over until I push power. Other times it will boot up fine and work fine. Last couple of days its booting up fine then crashing (shutting off) after a while. I ran Ultimate boot CD and mem test says the memory is fine but I suspect otherwise. The motherboard is ms-6378 with 1 gig memory and I changed nothing hardware wise. Also loaded optimized defaults in BIOS. I am at work and will continue with this in about 2 hrs I just wanted to put it out there to see if anyone had an idea for me. Thanks, Chris