If you can still manage to startup and login to Windows as normal, you could then carry out the instructions to run the chkdsk program from there. In that case you would not need to enter Safe Mode.
Just give it a go, it should be ok. If you make a mistake with the instructions dont worry, it should not 'hurt' anything and you can always try again from the start.
The next stage, if the problem persists, is to look at possibly uninstalling the Norton package followed by reinstall of Microsoft Security Essentials. Let me know and will try to assist with some instructions if you need them.