How do I make my Microsoft Word program stop deleting sentences I have already written?

I typed a report using Microsoft Word, and now whenever I try to add in text, the cursor will run over and delete my sentences! PLEASE help, this is a project and I can't work on it until I fix this problem!!!

How do I make my Microsoft Word program stop deleting sentences I have already written?
i am sure it is in OVERWRITE..can you see that OVR button next to the spelling and grammar status..click it twice and if it goes gray then you can type properly...you can see that at the very bottom..
Reply:Push the insert button on your keyboad on the top right part. This will prevent it from deleting the letters.
Reply:That happens when you have hit the 'Insert' Button. Its to the right on the keyboard... hit the button again to turn it off and your typing will go back to normal. Its simple.