Pressing F8 gets you into the Windows menus, you want to get into your PCs BIOS before that.
As soon as you turn on your machine, watch the screen and it should tell you to press one or more keys just about immediately to get into the BIOS. The usual key is the Delete key, it's the bottom left key in the block of 6 keys between the main qwerty keys and the number keys.
if it doesn't tell you, try tapping the delete key as your machine boots.
When you get into the BIOS go to the menu page where it shows the primary and secondary master and slave devices. Select each in turn and follow the menu selections for autodetection.
Once the machine has found the drives, follow the instructions to exit and save. The machine should then reboot and find the drives.
There should also be a menu in the BIOS giving the order in which the machine tries the devices looking for a boot disk. The older machines will just offer A-C or C-A (A = floppy, C=HDD). The newer ones will offer additional choices such as the CD drive. But they also normally autodetect the drives every boot.
I may be down in Saltdean tomorrow night, leaving on Boxing day. If you want, I can drop in. I'll drop you note with my mobile number.