You can buy laser printer cleaning pages at any Staples or the like. They are just sheets of 8.5x11 paper that you print a blank page on. While going through the printer it somehow cleans the interior. Don't ask me how, but I've had some luck with them. If the problem is real bad, you may have to repeat several times on more than one sheet. If you have trouble printing a blank page, type any letter(s) and change the text color to white.
Cliff