Here is my story (sort of long...sorry):

I have an issue with my home PC (Sony desktop, Win XP, about 8 years old). I installed some software that I now believe to be a virus. My computer started running slow right after I did it, and instead of running Spybot, AdAware, etc. right away, I rebooted. Well, right after that I received the following error:

Windows could not start because the following file is missing or corrupt:
windows\system32\ntoskrnl.exe
Please re-install a copy of the above file.

I then used the Win XP CD and recovery console to restore the "ntoskrnl" file. I also ran checkdisk, and no errors came up. I then rebooted, got to the logon screen (which by the way never used to come up) with my name listed. I don't have a password, so I clicked yes, my background picture pops up (but no icons). Now, as soon as that happens, it immediately says logging off, savings personal settings, etc. and goes back to the logon screen. (Note: I get this logon-logoff loop even if I try to logon in safe mode.)

My next step was to use the Win XP CD and repair windows. I reloaded Win XP on top of the original load and rebooted, but the same logon-logoff issue is there.

Also, a side issue is that I don't have a complete backup of my files, pictures, etc. so reformatting is out.

Help??

There are several suggestions in Ntoskrnl.exe is missing or corrupt.

You may be able to use a Windows XP bootable Floppy Disk to boot from a diskette instead of your hard drive. If your hard drive's boot sector or Windows' basic boot files have been corrupted, this disk will circumvent the problem and boot you into Windows. If you don't have an emergency boot floppy, you may be able to use one created on another PC running Windows XP but there's no guarantee that it will boot your machine.

How to obtain Windows XP Setup boot disks from Microsoft. The Setup boot disks are available so that you can run the Setup program on computers that cannot use a bootable CD-ROM.

If the emergency boot floppy does not work, try doing a "Repair Install with Recovery Console". The Recovery Console is a Windows utility that provides a DOS-like command line from which you can run some repair programs. If you have a Microsoft Windows CD-ROM, you can get to the Recovery Console by booting from that CD and pressing any key when you told to 'Press any key to boot from CD'. At the 'Welcome to Setup' screen, press r for Repair.