The computer may be overheating due to the system fan not working properly. If this is the case, you will need to replace the system fan in the computer. See the troubleshooting guide here: Troubleshooting Page

The optical drive may be defective or have a loose connection to the motherboard causing it not to read the disc. If the optical drive is bad then you will need to replace the drive. Check the troubleshooting page here: Troubleshooting Page If the connection is loose then open up the computer case and reseat the cable that connects from the motherboard to the optical drive. See troubleshooting page: Troubleshooting Page

The power supply might be failing or completely nonfunctional which will cause the computer to be unable to start. If this is the case then you will need to replace the computer's power supply. Check the troubleshooting page here: Troubleshooting Page