I assume that you are referring to DownLoad files, yes ?
A restart of the client will often help... and, used VERY infrequently, clicking on
Find More Resources can also help...
Also, remember that many, many, many people are connected to the internet via
dynamic connections which means, simply, that their IP address is 99% sure to be different every time they shut down and then re-connect... SO, you should do another search for your pending/incomplete DownLoads... You will probably find exactly the same person(s) sharing the same file(s) but with their 'new' IP... and then, voilą ! Download...
Isn't this fun ???