If you mean you are getting a STOP error that says something like:
SESSION3_INITIALIZATION_FAILED
*** STOP: 0x0000006F (0xc0000034, 00000000, 00000000, 00000000)
That usually means that the smss.exe file is missing - probably quarantined (effectively deleted) by some antivirus/antimalware program (Avast, AVG or avira! first thoughts).
You can recreate the problem anytime you want, then learn how to fix it.
There are several different SESSIONx_INITIALIZATION_FAILED messages and they all mean something different.
Generally not too hard or fix though.
For this one, I would do this:
After booting into the XP Recovery Console, you should be in the C:\WINDOWS folder. If you are not in the C:\WINDOWS folder you have some other problem that you need to fix first.
In the Recovery Console, from the C:\WINDOWS prompt, enter the following commands:
cd system32
copy c:\windows\system32\dllcache\smss.exe
Reply in the affirmative to any "are you sure" messages so 1 file(s) is copied then enter 'exit' at the command prompt (your system will restart)
Depending on your system configuration, you may need to copy the files from another location, so if they are not in the dllcache folder for some reason, enter the commands like this:
cd system32
copy c:\windows\ServicePackFiles\i386\smss.exe
exit
(your system will restart)
There are other possibilities for that message, but I would start with replacing the smss.exe file.