This has probably been observed before and may have been fixed in a recent version but I have foound that pLoader will not connect after accidently trying to load a video file.  I drag and drop whole folders of pictures into pLoader to upload to my Piwigo service and occasionally I include a .mp4 or similar video file. each time I have done this the pLoader stops working and will not reconnect. The problem is resolved by deleting the C:\Documents and Settings\myusername\Local Settings\Application Data\.pLoader folder (as found in one of your previous forums). I haven't found any reasons or causes for pLoader stopping  and not connecting in the forums but there are several citing the same problem.