Hi Monica; thanks for commenting.
That sounds to me like you need to make a small change to the 'Boot Order / Boot Sequence' in your computer's BIOS.
After you press the power button and the computer is whirring up, look carefully for a piece of text saying "Press 'X' to Enter Setup" (or words to that effect). The key you need to press is usually one of the F keys, or the Del key.
Once you work out which key it is, you will enter BIOS. In here you need to find the 'Boot Order / Boot Sequence / Boot Priority' setting (its called different things in different BIOS's).
From here you need to ensure your CD/DVD drive is listed as device number one. Make the hard drive device number two. Save these settings and try again.
Hopefully that helps - if you find yourself still struggling, let me know your PC's make and model number and I'll see if I can research it :-)