How do you make the print on your homepage bigger and darker?

Remember that I'm very computer challenged, so please bear with me. My sister just had a friend work on her computer, and now her Yahoo homepage is very compressed (only covers about half the screen), the print is SO SMALL AND SO LIGHT it is unreadable, and her toolbar that shows Home, Print, etc. is gone. Same goes for any site she calls up. WE CAN'T USE IT BECAUSE WE CAN'T READ OR SEE ANYTHING!! How can she make everything full size again, increase the size of the print, make it darker, and restore the toolbar on the Yahoo homepage? Your istance would be very greatly appreciated. Thanks very much!