Keyboard intermittent problems, spacebar and backspace?

The keys of the line starting with QWERTY and backspcace keys and the spacebar worked intermittently. I cleaned my keyboard with air pressure but the backspace key and spacebar are still intermittent problems. I have to press hard on the buttons to operate it. This problem occurred after changing my hard drive. I also replaced the battery with one from another brand. Sometimes I managed to resolve the problem by restarting the computer after removing the battery. But it does not always work!