Hello DeeBee, welcome to PCHF.
All valid points, the cable was my first thought, however it depends on the motherboard. It's always a good idea to use the cable supplied with the motherboard (if custom built). The cable you currently have could also be faulty.
Power supply is also another possibility and you will experience all kinds of wierd and wonderful symptoms when the PC is starved of power (not just with your cd-rom), or using a poor quality power supply. I don't particularly think this is the case with a 550w power supply, you would need an awful lot of powerful hardware in that PC. You can use a power supply calculator to get an idea of your PC requirements:
eXtreme Power Supply Calculator v2.5 (click goLite).