There are many similar community threads on force.com discussion boards around the same issue “No Debug logs” issue.
How to fix this ?
This issue poped because of a bug in winter’11(20.0.0) Force.com IDE. The Force.com IDE team released an IDE update(20.0.1) on November 15, 2010 that addresses this issue. More details in screen shot below and IDE release notes page here.
So, to get rid of this issue, just update your Force.com IDE via this update site : http://www.adnsandbox.com/tools/ide/install/