Wait until Limewire is fully started up and sharing the correct number of files. Go to Limewire Library-> Incomlete files -> highlight the desired file and click resume.
In theory this should hopefully reconnect and continue downloading. BUT it depends if anyone is online with the file and you may have to wait hours or weeks for someone to come on line with EXACTLY the same file. You might be better off re-searching for the file and doing a fresh download
If a file is overdue on your settings for "days to keep incomplete downloads" afaik it is deleted without futher ado .I'm not sure about this as I have my limit set to 300 days and haven't encountered the problem
In these cases, I'm fairly sure you need to make a fresh search for the file, but in any event you would need to start from zero
I hope this helps.