There's no central server...you download by connecting to other computers. So...if people go offline that can disrupt downloads. If people don't have any free upload slots, that can disrupt downloads. As new hosts for files come online, downloads can start up again etc.

Files which sit connecting for ages & then need more sources but never begin downloading are likely fakes. Check the sticky below for more info
Fake files showing up in search results

Your download speed depends on your connection speed, host(s) connection speed, how many upload slots the host has open, how many hosts you're downloading from, how well you & hosts have their LW configured etc etc
Try the tips below for setting up your LW
Configuring LW for best performance