Blue Screen, last known config and safe mode won't work

[travelocutor]

Home network consists of this Dell 8300 on which I'm typing and wife's Dell 8400 that will not come up.  Two weeks ago I installed a scanner and the software that came with it on the 8400; a trial scan of a magazine cover came through just fine.  A day or two later, we got the BSOD with message:
C000021a Unknown Hard Error
I tried last known configuration that worked and got the blue screen again; then tried safe mode and, again, got the blue screen.  Just now tried to start up again; DOS screen came up with message about shut down to protect files or failed startup, giving me the "last known" and safe mode options; I selected "last known", got the XP copyright screen with the little blue crawler for about 90 seconds, and then the familiar blue screen:
A problem has been detected and Windows has been shut down to protect damage to your computer. 
PROCESS1_INITIALIZATION_FAILED
  Yadda-yadda about hardware/software installation and using safe mode to restart...
Technical information:
**STOP: 0x0000006B (0x0000007A,0x00000006,0x00000000,0x00000000)

Since I can't get the 8400 to come up, I can't give system info.  It's pretty much the same as the 8300, probably with a faster CPU and more storage; I know it has 2GB of RAM.  Thanks for your help

[travelocutor]

Sorry about that; apparently three spacebars equals "send" on this site.  Anyway, as I was saying, that blue screen goes on to advise me to remove new hardware or software and use the safe mode (which won't respond for me.)  The technical info at the bottom of the screen is:
**  STOP: 0x0000006B (0xC000007A,0x00000006,0x00000000,0x00000000)
There are a number of other posts about the blue screen, but I can't find these code numbers anywhere so I'm making a new post.  I apologize if this is a repetition for you folks, and thanks in advance for your help. 

[midsail]

Try starting in Safe Mode, start up the pc and press F8. If it starts in Safe Mode this will tell us it is a driver conflict, just remove the software.

[travelocutor]

Thanks, Midsail; sorry I wasn't more clear about the problem.  I've tried both safe mode and last known good config, and neither one of them yields anything but the blue screen.  Unless there's another way to call the safe mode (besides the F8 key at startup), I'm stumped.  My wife found person at her IT department who's agreed to take a look at the machine, and hopefully he'll be able to resolve the problem and teach me a little something in the bargain.  Please consider this thread closed for now; if the helper can't help me, I'll come whining back to this forum then.  I'll also try to remember to post the results if he does solve the problem so other people can find the solution.  Thanks again.