the faq of lw 5.12 and the latest say ---- If the incomplete file is still on your computer but does not appear in the list of downloads, go to the Library, click "Incomplete Files" and then resume the download from there.

where is the Incomplete file option in the library?

Right-click the file in the library. I presume you can use the Control key to select multiple ones at same time. However, I'm using LW 5.2 & I do not see any such options for my incomplete files. I did not think LW 5 had the option to continue incomplete files that refuse to load.

The only process I'm aware of is to revert back to LW 4, select the incomplete files in the Library & press Resume button. This will force them back into download window. Then you could close LW, upgrade back to LW 5. There is a sample image about how to do this here Downgrading to LimeWire 4 from 5 & resuming incomplete downloads.

the reason i can't degrade to lw4 is that in it, it need user interference when it starts and continue after user responds to update to the latest version.
And as i use task scheduler to start lw from 12-7am. Only during that time my download is not chargeable.

And also if i copy the incomplete file from incomplete folder. Can i continue them in a different system

Yes you can continue them from a different system, as long as you include the incomplete folder & the downloads.dat file.

yes thanx,
if i want to continue file later i have to just cut those related files to a different location and paste them there later if i want to download one file at a time. b,coz cancelling download will completely remove it and you have start again from the beginning.

To do it on a different system: install LW, close the program. Then replace both the incomplete folder and downloads.dat file with your older one from other system. The downloads.dat file needs to go into the LW preferences folder if you are using LW 5 (or 4.18). Or into the incomplete folder if you are using LW 4.16
I must emphasise this should only be done whilst LW is closed.