What ver. of TD are you using? What automated tool are you using? Have you highlighted the test in the Grid? From the test plan, can you see the entire test from the Test Script tab? When you select run, do you see anything at all change?
Are you trying to run the tet on the same machine that you have TD opened on? I assume that you have QTP installed. If you are trying to run the test on a remote PC there have been several issues with that process. Is the icon infront of the test in the Planning area different from the non-QTP tests. Is it a question mark? if it is not different or a question mark, then QTP is not registered with TD.
Wait a minute, I don't believe QTP 8.0 will run at all with TD 7.6. You might want to check with your Mercury Rep. on at the Mercury support sight.