fix computer errors

HP Computer
Windows XP Home Edition
First, I thought our monitor was going out. Finally, one morning, we could turn the computer on, but see no screen, except when it was unplugged from the tower itself, where it clearly displayed “Check Signal”. Turns out that, among other things, the video or graphics card was out. So, they replaced the video/graphics card (actually put in a second one since my original is built-in) and fixed the screen problem, but now, Windows will not start up at all except for in Safe Mode/Safe Mode with Networking.
If I try to start up in normal mode or in Last Known Good Configuration, it goes to a black screen after displaying the windows logo and the scrolling blue bar. It’ll sit there and do nothing. Last night, I got it to work on Last Known Good config. because the mouse cursor appeared, so I pushed Ctrl+Alt+Delete and it started up after it performed a 5 stage checkdisk. Unfortunately, my mother put her Diablo II game in and it crashed it. Now, this morning, it’s back to only working in safe mode.
I DID get the error that says “Windows could not start because the following file is missing or corrupted: System32\Drivers\pci.sys
I went and changed the settings for the computer to load up the CDROM drive before the hard drive, used my Windows XP Home CD to expand the file from D:\i386\psi.sy_ C:\WINDOWS\SYSTEM32\drivers /y. It still would not start up. I received the error again, so it must not have worked. I tried to perform the full checkdisk again, but it didn’t work.
It will also not open in Debug mode. Black screen response for over a half an hour.
I tried going to the device manager and decreasing the hardware acceleration. Didn’t do a thing.
Screen resolution is just fine.
In the Device Manager, nothing is coming up as corrupted or needing updates.
I’ve searched all over google and done all of this, and it still will only boot up in Safe Modes.
Is there anything in my regedit that I should look for? I read that I should look in HKEY_LOCAL_MACHINE\Software\Microsoft\Wi… Version\Winlogon\Notify to check and see if anybody installed anything in there, but what exactly do I look for?
I cannot run the winnt\32 /cmdcons from the i386 folder of the CD for some reason.
The NeoComputers store also gave me MalwareBytes and Spyware Terminator to run on the computer last night, but it didn’t come up with anything that wasn’t a false positive (i.e. PopCap game data from the MahJong that my mother bought from Yahoo).
What caused this, and what else can I do to fix it here at home so that I can avoid paying $65+ per hour for them to root around my files?