Got a lot driver problems please help.

[Effekt]

Okay, well I was trying to fix my buddies computer, because his CDROMs weren't working, so I was reading up on how to fix it. Well, their was one method that said too delete upper limits and lower limits of a file which I forgot now. Now, their was a couple of these folders that were named the samething so I did it for about 7 of the same folders....and well the mouse and keyboard were working at the time even after I deleted. Then I restarted and I got some message saying the hardware or whatever was found and installed, I need to restart the computer for it to be in effect, well I did and the mouse and keyboard didn't work anymore from then on. They work still on the page where you can do a system recovery, setup and stuff like that. I tried to do a system recovery but it won't work, everything else will though. Does anyone please have a solution? I feel so bad for messing it up even more for him:(
I also know I'm still new, but guys I promise you I will become more part of this community, as I need tech help every once in a while anyways.

[Thrax]

Can you perform a repair install on the system? That's the only thing that can fix it at this point. Or a reformat.

[Effekt]

Can you perform a repair install on the system? That's the only thing that can fix it at this point. Or a reformat.
What exactly is that and how would I do it? I'm not that great with terms sorry.

[kryyst]

You boot up the computer with the windows xp cd in the drive. You then skip over the first screen where it asks you if you want to go into repair console and proceed like a normal install. It'll detect that you already have a copy of windows installed on that machine and ask if you want to repair it. At that point you tell it yes. It then goes through and resets all the core system files. He won't lose any installed programs or data or anything. It just resets windows back to default.

Of course it'll also ask you to re-register windows so you need to use his windows disk and not yours if you want to keep it legal.

[Effekt]

You boot up the computer with the windows xp cd in the drive. You then skip over the first screen where it asks you if you want to go into repair console and proceed like a normal install. It'll detect that you already have a copy of windows installed on that machine and ask if you want to repair it. At that point you tell it yes. It then goes through and resets all the core system files. He won't lose any installed programs or data or anything. It just resets windows back to default.

Of course it'll also ask you to re-register windows so you need to use his windows disk and not yours if you want to keep it legal.

Oh awesome, even though his CD drive doesn't work, it would read this still or what? Also, what is exactly the cd called? I really appreciate your help guys.

[Thrax]

The CD is called Windows XP. You know the operating system? :) Without it, you cannot repair this PC.