the Speening Wheel Appears No Programm Runs


I have a Powerbook G3 series running on Mac osx 10.3, lately i have installed some fonts, when i started my computer again the speenig wheel appear , the finder won't stard at the top of the screen the taskbar dosen't appear , when i click a programm icon like safari or system preferences it won't start, nothing seems to work. what should i do, i don't know any commands how to access any meniu, i 'm a windows user and with appele i'm stucked