You must enable available workflow list from profiles ( administration -> profiles -> first tab). Also to start any workflow you need to doing it selecting a document.
In addition if your problem is that you're not showing th form just when you start workflow then take in consideration, there's an special task name in forms.xml if you want to be shown the form at the moment you're registering. You can see example in this form with task called task="run_config":
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE workflow-forms PUBLIC "-//OpenKM//DTD Workflow Forms 2.1//EN"
"http://www.openkm.com/dtd/workflow-forms-2.1.dtd">
<workflow-forms>
<workflow-form task="run_config">
<input label="number" name="number" />
<button name="submit" label="Submit" />
</workflow-form>
<workflow-form task="task">
<input label="number" name="number" data="modified" />
<button name="submit" label="Submit" />
</workflow-form>
</workflow-forms>
Here you can find some examples http://wiki.openkm.com/index.php/File:Course_workflows.zip, also I suggest take a look on it. Hope this could be useful for you