Keyboard Scroll Lock Problems

Having a problem with my keyboard I hope one of you can help with.

First noticed it on then arrow keys, but is now happening on all keys:

- If i hold the arrow down to scroll the page it only moves down one step and then stops (no scrolling).
- If i hold down a letter on the keyboard, instead of getting a stream of the same letters (eg. aaaaaaaaaaaaaaaa) i just get the letter once despite holding the button down.

Is there any kind of scroll lock or anything like that i could have turned on my mistake? Am using an imac (version 10.6.8)