Safe mode booting

Hello,
I was trying to go into safe mode to run virus software. Computer (XP) would not open in safe mode. Received advice to go into msconfig and change tab to "start in safe mode"
Now computer repeatedly restarts, but each time it restarts and tries to go into safe mode--which of course it will not do. I do not know how to get back into msconfig and change back to original setting.

I get the screen telling me that windows did not start successfully.
Every option
safe mode
last known good config
start windows normally

all restart and he process is repeated again.
Any help we would be greatly appreciated.
Rich