My Nokia N81 is having a texting problem. Help?

Hi so my problem is this: When I try to type in a letter, for example "n", you are supposed to click the 6 key twice, but it comes up as "On" and its underlined. if i type the 7 key 5 times, i get "Spr?" underlined and it wont let me type another letter and it just beeps. what is wrong with my texting?