I have no OS on my computer and I am tring to install windows xp however i cange change boot sequence.?

I bought a Dell computer with no OS from E-Bay. When I tried to change the boot sequence for it to read the cd rom it will not let me. I pressed F1 for help and it said to to press enter to change however when I press enter it will not let me change it. I am not too computer smart So I was wondering if anyone knew what may be wrong with my computer or what I should do?I have no OS on my computer and I am tring to install windows xp however i cange change boot sequence.?when booting up, press F2, then hit the -%26gt; key and scroll over to boot and change the boot sequence.I have no OS on my computer and I am tring to install windows xp however i cange change boot sequence.?It's NEVER a good idea to buy a computer without an OS. Unless it was dirt cheap. This means you have to do a clean install. And that means buying a brand new CD-ROM for XP. You will have problems if you try to install the same XP CD-ROM on two computers. XP is now out-dated. If your new computer has the speed and memory to handle it, I'd go with Vista.