Trying to boot an old dell 4300

I am trying to get my old dell 4300 series to work. When I turn it on it tells me. Windows could not start because the following file is either missing or corrupt.

\Windows\System32\Config\system.

Then when I go into the windows setup using the f12 key right when the windows first starts it asks for a password. I can not remember the password. Is there anyway to fix this. Also If I need a whole new Windows XP disk. I do not have one. I am wondering if there is anyway to get the whole XP file somewhere online and burn it to a DVD? I do have a CD. It says Dell Optiplex Resource CD. But it says for drivers and utilities already installed on your computer.

Contents
Device drivers
Diagnostics and utilities
online documentation.

Is there anyway to fix this at all.

I have installed a new HDD on the computer I still have the same old HDD it originally had. But I put another one in.

It is a Dell 4300 series. Year 2003

I never installed the Os. It was on the PC when I got it. It is so old I know nothing about it honestly. Accept that I took it all apart put a new CPU in it and a new hard drive. more RAM. but that is it other than that. I just need that CD to finish it I believe. that is all. I am almost positive that is it all good I just need to reinstall XP is all. I wish I knew somewhere I could juts get a New XP disk. I have another PC with XP on it that works. But I need CD's to make a XP repair disk. I think I am going to try that. I think it still works anyway.

okay. I think that is what dell told me. That I need the full XP not the repair. But thank you. There is no where to get it online obviously.