I don't believe you can use the debugging tools when launching QTP scripts from QC. Doesn't the Run Results report for QTP give you any useful information? You could also add Reporter statements to your script to write more info to the Run Results report.
I had a situation where QTP would crash and there would be nothing in the run results. I made a manual log function to see which line was last executed and therefore find my trouble maker.
Function DebugLog(filepath, data, append)
If Len(Trim(data)) > 0 Then data = Now & Chr(9) & data
DebugLog = Empty
Set objFSO = CreateObject("Scripting.FileSystemObject")
If Not append And objFSO.FileExists(filepath) Then objFSO.DeleteFile filepath
Set objTextFile = objFSO.OpenTextFile(filepath, 8, True)
If objFSO.FileExists(filepath) Then objTextFile.Close
Set objTextFile = Nothing
Set objFSO = Nothing
Call this function around your script/actions/code to try determining where issue occurs and more: