Read http://www.tomshardware.com/howto/20040122/ to see if you have enough power. After you figure that out, consider that what's on the label is likely an outright lie. http://www.tomshardware.com/howto/20021021/ shows that too many didn't meet their own specs.
Reading your post, all the good information about the machine is void.
Every now and then when I turn on my computer, I get an OS not found error. I use my computer everyday and I would say this happens about 1-2 times a month. My first thought was intermittent power supply problems. Anyone else have any ideas?