Windows wont boot

I have a PC here that had win 95 on it and was upgraded using a win 98 upgrade. It started up ok until somebody went into the bios and chose “Default set up”. Ever since then it wont boot to windows it just hangs. i can get into safe mode and I have tried different setting in msconfig but doesnt help. I have tried different changes in the bios but that doesnt help either.
Please help.