You need to access your BIOS during first boot. I am not sure how to get into the BIOS on a Compaq Presario. On most (home built types) we just hit delete several times as soon as the boot process begins, but some factory made computers like your compaq have a different key to hit during boot...sometimes I think 2 keys.. the BIOS is a pre programmed ROM chip on the motherboard that has a small amount of software to help the processor "find its way" when first turned on.
If you can get into your BIOS (Basic Input / Output System).
http://webopedia.internet.com/TERM/B/BIOS.html
In the Standard CMOS setup screen you should see your hard drive as master on the primary IDE controller... possibly a CD drive as a Slave to the hard drive. Or...they could both be setup as master and slave on the secondary IDE controller. If you do not see your drives showing up as being setup for these controllers, we must then determine why and correct it.
I suspect there are there and setup properly in your BIOS..there has been several people posting that their CD optical drives disappear from Windows XP. (Is that what you are using)?