when you restart your machine, watch for a message stating press key to enter setup, once in bios setup look for the menu containing the ide channels, should list primary master, slave, secondary master, slave. Set the channel the cdrom is connected to accordingly\
If you don't see a message here is a list of common keys to enter setup
Entering CMOS For Different Motherboards
Press Tab during boot=Emachine
Press del during boot= (AMI, Award).
Press Esc during boot= Toshiba.
Press F1 during boot= (Toshiba; Phoenix; Late model PS/1 Value Point and 330s).
Press F2 during boot = (NEC).
Press F10 when square in top RH corner of screen= (Compaq).
Press Ins during boot=IBM PS/2 with reference partition.
Shift Ctrl Alt + Num Pad del= - Olivetti PC Pro.
Ctrl Alt ? =some PS/2s, such as 75 and 90.
Ctrl-Esc = Misc Puters
Ctrl Ins= some PS/2s when pointer at top right of screen.
Press reset twice= some Dells.
Ctrl Alt Enter= Dell.
Ctrl Alt Esc=AST Advantage, Award, Tandon.
Ctrl Alt + =Misc Puters
Ctrl Alt S= Phoenix.
Ctrl Alt Ins= (Zenith, Phoenix)
Ctrl S =(Phoenix).
Ctrl Shift Esc= Tandon 386.