Support Restoring old Dell Desktop to Factory Settings w/XP

So my uncle recently got himself a laptop and gave me his old desktop to do...well, whatever I'd like with it. He wasn't very tech savvy and the thing's kinda crappy. I mean, it isn't horrible, just not well-taken care of (seems like it has some forms of malware on it at the least). I backed up and transferred all of the files he wanted to keep, mostly pictures. I'm now trying to make the thing as new as possible, though it'd still be heavily dated.
So long story short, I'm trying to wipe the thing clean by restoring it to factory settings and then upgrading the OS since it's still on Windows XP.
I have none of the original discs or anything since he's gotten rid of them years ago. There's no warranty on it or anything, but I should still be able to reset it to factory settings, right?

It's a Dell Dimension 3000 with Windows XP.
I've never done reset a desktop before, but I thought I knew how. Evidently, I don't. I tried pressing F1-F12 while it was booting, Ctrl+F11 which I keep seeing pop up everywhere, but no luck (or at least, I can't find the options to). System Restore only goes back a few months, not to factory default settings.

When it boots, I do get a screen that prompts me to either continue booting by pressing F1 or to run the setup utility by pressing F2 (note: Couldn't find a way to do it through the setup utility).
The whole screen is

Spoiler

Phoenix ROM BIOS PLUS Version 1.10 A03
Copyright 1985-1988 Phoenix Technologies Ltd.
Copyright 1990-2004 Dell Computer Corporation
All Rights Reserved

Dell System Dimension 3000 Series
BIOS version A03
www.dell.com

Secondary drive 0 not found
Strike the F1 key to continue, F2 to run the setup utility
_

The system is Windows XP, version 2002, Professional edition with Service Pack 3.

There is literally nothing of value left on this computer; I just need it as fresh as possible before I update to a newer OS. I don't know if I do need a setup disc, but I don't recall having needing one when I reset an old laptop (unless desktops are different or if it's just the year/model of this one) and I would like to avoid having to pay for one. Maybe I'm less tech-savvy than I thought and I just can't figure it out when it's obvious, but any help would be appreciated.

 

You'll need a Windows XP install disc. Newer computers that run Windows 8 have a system refresh option but that's really the only way to reinstall an OS without the necessary discs. If the thing is really badly bogged with malware or whatever, I'd recommend running something like Darik's Boot and Nuke to make sure the hard drive is clean as a whistle and then clean installing Windows XP. Just make sure you know the XP product code (there should be a sticker on the tower with it).

If you don't have XP install discs, you can find an ISO online pretty easily, burn it to a CD, and then run it off there. Sometimes you can run it off a flash drive but older mobos don't always support it.