No explorer.exe, no desktop, unable to loade explorer.exe

I have a problem that started I guess a week ago. First I noticed that North's Utilities reported that core files had changed -- reinstall program. Then the program ran as usual. Like a dummy, I did nothing.

Then today when I was booting up, I noticed an error : Windows cannot find the following files in the C:\Windows/INF/ folder ( msnetmtg.inf, msmgs.inf wmpll.inf and fxocm.inf).

Okay, I rebooted and got a blank desktop, there was no icons on the screen, could not get to quick launch toolbar at bottom of the page. The only thing I could do was alt-crtl-del The Task manager opened and I tried to to start explorer.exe it appear and quickly disappeared. I can go to new task, type in explorer.exe and it will appear for about 5 seconds and disappear.

So at this point all I have is a yellow screen which is the background color, no icons, no quick launch bar, no nothing. I suspect that I have a bad infection. Also, I tried to do a system recovery, no system restore points are available. I even tried to reinstall windows and got a message the start windows normally and then insert the disk and upgrade from without windows. Since I cannot access anything from windows normally, cannot upgrade or reinstall Windows over the current installation.

I cannot run any program because I cannot get explorer.exe to load.

Can you help?
Thanks,