Check the user info of the person you are trying to download from. They may have set some rules they want you to follow before they allow your downloads to start.
Or, the user you are trying to download from may just have a lot of other people downloading, maybe some slowpokes who are hogging upload slots. There's nothing you can do but be patient. You should see your place in line changing over time, at least. Donating does help bump you to the front of the queue, but it doesn't solve the problem of other people just being slow.
Your port forwarding may not be working, or their port forwarding may not be working. This makes it difficult to get downloads to start. In SoulseekQt, under Options > Login, click the Check Ports button. If your ports are reported as "closed" then your router is not accepting Soulseek connections from the outside world and passing them to your Soulseek app. You may be able to manually configure the router to port-forward; Google the model of your router and
port forwarding. If you are on a school or company network, though, or if your ISP has you on a CGNAT type of network, you may not be able to port-forward at all.