I just have one hard drive, and unfortunately, I don't know anything about partitioning or whether my hard drive is (I didn't install it; it's the original that the person I bought my PC from). If I'm understanding your question correctly, no, I don't have my OS installed on it's own drive; it's with everything else.
I've tried to reinstall Windows several time, but the prompt for installing doesn't appear when I put the disc in.
(I hope I'm posting this correctly; I couldn't find a button to reply to your answer.)
1.start the system (DO THIS WITH YOUR WINDOWS OS DISK INSERTED)
2. on the BIOS screen enter the boot menu by pressing f10 or f9 or del or any other key, the keys will be displayed on the bios screen.
3.in the boot menu, your HD, your DVD ROM,USB and 1 other thing will appear.(i didn't remember the name).
4. leave all and just click on the DVD or CD whatever is written on your boot menu screen.
5. black screen will appear with written attempting boot from CD.
6. when there will be dots blinking, press any key.
7. Surely installation of OS will start.