Having dealt with this issue many times in my life (and still currently having to deal with it on and off) I would agree with what others said and say, "just draw!"
But I realize sometimes that advice feels pretty obvious, and unhelpful, so here are four things you could try:
1) [if you enjoy playing video games and writing] : Find a video game you can play which lends itself to keeping an in-character diary. Play the game for a limited period each day and write in the diary daily as well. As you write also illustrate WHAT you're writing about. Draw things you see in the game, never use screenshots just draw with the game running (unless the game is of the kind very much not conducive to this). This is a difficult but highly useful project, I'm working on my own currently using the Elder Scrolls game Morrowind.
2) Get yourself a Reader's Digest, not the magazines but the book kind that contain several short or abridged stories. Go through the pages seven at a time each week. Scan each page for a word, phrase, or sentence that catches your interest and underline it. After you do this go through the pages again and put a layer of gesso over all of the page EXCEPT the words you underlined. Once it's all dry (and this does take a little time - hairdryer makes it go faster but be careful) go back and illustrate in some manner (abstract, concrete, however you like) the words that you left on the page.
In Illustration II in college we did this project and it's a very good way to improve your skills as well as providing you with a springboard for your imagination.
3: Take a book and read it ten or twenty pages at a time, then stop and try to illustrate (NOT in the book like with the Reader's Digest, on some other surface) a major scene or event that occurred within those pages. While this is similar to the Digest project it differs in that your illustrations are restricted to relating directly to the actual content of the book. In the Digest you may illustrate things however you like, they need have nothing to do with the stories the words come from (in fact it's better if they don't).
4: Finally, if your desperate to avoid the rigorous structure of the above three (because they have the best results when done in a consistent day by day fashion), find music or film or novel that inspires you, and work from there. If music is your thing I recommend using Pandora radio, it's free and you can basically create a station that is limited to only the most inspiring kinds of music. I use it when working. If stories inspire you to art, try your library for audio books (because you can draw while listening and I personally find that helpful) or a site called Relic Radio (old radio dramas of many genres are there, free. You can also access it through iTunes).
I hope you find some of that helpful. I understand how frustrating it is when it seems like you just can't draw, I do hope you get over that quickly.
[color="SeaGreen"]E-aro Rejkhia lekjyr...[/color]