Sorry if this has been asked before, but I feel like my situation is a bit unique. I built my computer without enough left over for windows 7, so I installed it using an old re-installation disk. However, because the Product ID and key was ingenuine, I had to buy a new copy. So I bought a system builder's oem.
How would I go about formatting the current hard drive with windows installed?
Can I boot up from the OEM disk and format the hard drive from there? And if so, how would I go about doing that?
You can either go into the BIOS of the computer (normally done by pressing F2 or DEL) and change the boot order so that the CD/DVD comes first and then reboot with the disk in; or you can press the button that will bring up the boot menu for your computer (it will usually be on the BIOS Splash screen and is typically F12) and then just choose the CD/DVD drive from the list and you're off.
The rest is self-explanatory.
There is information . HERE
about doing the reinstall and what steps to take if you get stuck.