I've heard of rare occasions of this happening before. The only idea I can think of to resume them would be to downgrade to LW 4, resume, then upgrade back to LW 5. Unfortunately LW 5 has no resume function for incomplete files.

ie: in LW 4, click on Library, click on incomplete files tab on left side near bottom. Now select all & press the Resume button. This will force the incomplete files back into the Download window.

BTW there is no guarantee that the incomplete files will resume from their previous %, but in any case, they will all show 0% until they actually start downloading again. After upgrading LW again, I'd recommend doing searches to try to find sources to download from.