If it is only in the Downloads window that the files show zero, then hopefully the Downloads.dat file has not been totally corrupted.
In my experience, 'if' you can get any of these to start again, they will resume where they once were and show their original download percentage.

In LW 5 if you cancel the download file it deletes the incomplete file. In LW 4 & I think FW, it does not do this. How I resolved this in LW 4 was (2 ways, the 2nd listed as my main approach),
(1) if the file did not start automatically after finding the file in search results (ie: it did not recognise the file as downloading), I could cancel the download from the download window, then re-choose from the search results.
(2) Cancel all my downloads from the download window, then go to the Library -> incomplete files window, select all & click the Resume button. This would force all the files back into the Downloads window. Some might mysteriously start on their own. But basically most needed to be backed up with individual searches to find sources for them. This generally worked for many/most files.

However, a couple weeks ago whilst using LimeWire Pirate Edition, the HDD my downloads go to decided to dismount. LW then decided to totally wipe my downloads.dat file because it could not find the location. I was unable to get these to continue & bit my lip and started from scratch (deleted the incomplete files.) Highly annoying of course. I had one 1.8 GB video file that was over 80% complete. (I had over 200 GB of incomplete files.)

I think LPE (LW5) works a little differently with the downloads than either LW 4 or FrostWire which are similar in many ways.
(BTW applauds for finding a similar/identical topic.)