If that's the case, put your Windows install disc in the CD/DVD drive and after booting with the F12, select it to install Windows. Then be prepared for a plethora of Windows Updates when you get it installed. Prior to that I'd go to Dell's web site and download the specific drivers and helper apps you'll need unless you already have them on a disc.
I have a dell I put a new hard drive and replaced the CMOS battery I bootup and I see an option to hit f12 to enter bios it says onboard or usb cd-rom drive,system setup,hard drive diagnostics and boot to utility partition I can select any of these options but not sure what to do? If I boot and don't hit f12 I get floppy diskette seek failure hit f1 to continue and that just repeats itself. I'm stuck please help. Thank you