Since you can not lock your PCI bus there is a good possibility that you have corrupted data and need to perform a "Repair" of your Windows installation.
Are you running Windows XP? If so, here is how to perform the "Repair". You will not lose your programs, personal data or settings with a "Repair".
Boot the computer using the XP CD. You may need to change the boot order in the system BIOS so the CD boots before the hard drive. Check your system documentation for steps to access the BIOS and change the boot order.
Reboot your computer with the Windows XP CD in the CD drive.
The following message will appear on a black screen with white letters:
Press any key to boot from the CD.
Press the <Spacebar> to boot to the Windows XP CD.
After several moments of initializing some modules, the Windows XP Setup screen will appear.
When you see the "Welcome To Setup" screen, you will see the options below:
This portion of the Setup program prepares Microsoft Windows XP to run on your computer --> To setup Windows XP now, press ENTER --> To repair a Windows XP installation using Recovery Console, press R.
Do NOT press R
To quit Setup without installing Windows XP, press F3 and Press Enter to start the Windows Setup.
The Windows XP Licensing Agreement will appear --> Press the <F8> key to agree.
Setup will search for previous versions of Windows and find your previous installation that you wish to repair.
The prompt will be:
If one of the following Windows XP installations is damaged, Setup can try to repair it.
Use the UP and DOWN ARROW keys to select an installation.
To repair the selected Windows XP installation, press R.
To continue installing a fresh copy of Windows XP without repairing, press ESC.
DO NOT PRESS ESC. Allow the installation to continue and repair your system.