I got some computer components today to build a basic computer. I put everything together (mobo,processor,fan,hdd,cdrw,dvd,video card).

I built my friend one just like this but w/ a different mobo.

My problem is that it will not start. I plugged it in and had the keyboard, mouse and monitor plugged in. It turned on momentarily (maybe 15 seconds) and said something about CMOS and low battery... i could not really catch it as i was making sure all of the components in the computer were turning on.

What may be the problem? I am stumped the computer will not start anymore at all.