I suppose Norton AV didn't cause the trouble : I had it for several months onto my machine and it didn't modify anything into Win95, except leaving its keys into the registry, you know the Win's trashcan...

Did you have a look to MSDOS.SYS into your HD root dir ? Perhaps there's an undocumented Win95 command to prevent from DOS booting, like BootGUI = 0 to boot under DOS prompt, and = 1 to start Explorer.

Another idea : I remember an article (into PC Mag perhaps) which explained how to make disappear the possibility to boot under DOS, with a registry entry... I will seek for it, ASAP.

Regards