What do you mean unable to restart downloads? Do you mean they don't begin by themselves or you get an error message saying unable to load old incomplete downloads? If the latter then try:

Try these: Fixes for Limewire & before next time you turn you computer off, make a copy of the download.dat & bak files which can be found in the incomplete folder. Then after rebooting & opening LW, if the same problem, close LW & replace those download.dat & bak files with the copies.

Otherwise tell us more details.