It's true that there are many ways to generate income online with no cash. But remember whenever you take cash out of the business equation, you must add time. As a rule it will take much longer to earn a decent income with zero investment.
The real money in most Paid To programs comes from referrals. Getting huge numbers of referrals with cash is difficult - without cash investments in advertising, it becomes even more difficult.
You can try:
* Free classifieds
* Forum marketing
* Article writing
Best thing is to start with even a tiny investment of say $5 a week and focus on ONE endeavor.