can you get into the bios by tapping f2 during bootup ?
It's not F2 for every computer though, and, he already said he changed the CD Drive to boot.
Xwardos, are you getting any beeps?
Try disconnecting everything but the main hard drive. Power and data cables. If that does not fix it, take every stick of RAM out, and put it in the first bank (it should be labeled as 0 or Slot 0 or something similar). If it doesn't work, put it one bank down, keep doing that for as long as it does not work, until you reach the last bank. Still not working? Go through the next stick of RAM, until you are through them all. This is to test if your RAM is giving you hell. Get back to us once you are done.