iMac starts then screen goes black

iMac Intel EMC 2134

So I adopted a free, non running Intel iMac 24 from my job. It stopped working just outside of the warranty period and it was decided that it wasn't of use to them, so it got tucked into the back room for a long while. Since I work in the business of information, the HDD was removed prior to me taking it home. So I put in another HDD, removed to logic board to see if there would be any visible issues on it (I've heard of the g5 caps...). I didn't see anything so I put it back together. Now the very first time I turned it on, I got a chime, then it turned off. So I started it again. This time I got a white screen, so I stuffed in the install disk, I saw the apple logo and ran off to get a usb keyboard and mouse (I don't have the ones that came with the machine). When I came back, the screen was black and the only thing running was the DVD drive. So I unplug, hold power button for 5 seconds, plug it back and start it again, now the only thing that will happen is that the DVD drive runs, nothing else. I have LED's 1-3 illuminated when this happens. I am leaning towards it being a bad logic board, but would like some other opinions.