Its possible that the first boot device set in the bios is the CD Drive, and now that its gone it may be making the system stop rather than looking for the next device. Usually that doesn't happen, however its a possibility. Also it could be that the Hard drive was sharing the PATA cable with the CD-drive and you may need to check the jumper settings or position of the drive on the cable. If the jumper on the drive is Cable Select make sure that the drive is at the end of the ribbon cable, if that doesn't work and the drive is on the cable alone move the jumper to the Master position ( or if there are 2 drives make sure the one at the end of the cable is set to master and the other one is set to slave, or both to cable select). I don't know if this will help or not, but its worth a look anyhow. Good Luck!