(matter of fact almost always helpful) to state the EXACT error message encountered.
Without knowing more it is difficult to say but the following link may be helpful -
http://support.microsoft.com/default.aspx?scid=kb;en-us;q307545 (or http://www.kellys-korner-xp.com/xp_sys32.htm )
If you can boot to Safe Mode (keep pressing the F8 key while booting) you might also try selecting the "Last known good configuration".
If you can boot to the Floppy drive but not to the CD (what I gather from your post) you might need to go into your CMOS setup while booting and change the boot order.
I have a system error which is not allowing me to boot. keeeping getting message about missing file. \winnt\system32\config\system. I have try to reinstall windows xp but cpu not reading disc in cd drive but will read off floppy drive but I dont have a floppy with missing file. any help would be greatly appreciate.