its possible that your CD drive cable is loose and or your SMPS is weak, just try to check the cable and try getting a greater watt power supply.. as when 100% usage is there, the system consumes more power and your pc is unable to give adequate power to the CDROM.. and you can also try to check if your system is infected by any virus or all system files are ok or not..
but main reason is power.. that i am sure about..