Problems With iPhone 4 Keyboard

My iPhone 4 keys are hard to press. I literally have to press hard on them sometimes in order to make them insert the letter. (Not all the keys do this, just some). And also, when i press certain keys, itll insert another letter. For example: If i press the space bar, itll insert the letter X, or if i press the letter L, it will insert the letter O. And my fingers are nowhere near the letters that im NOT intending on pressing. Ive done 2 full restores, but it hasnt solved the problem. Is anyone else having this problem, and can anyone help me resolve this? Thanks in advance!
Dell Windows 7