need help with external drive not showing up on desktop

If you plug either of the drives directly to your computer, do they appear? If not, are they optioned to appear under your Finder Preferences? If they still do not appear, I would next go down under the Apple menu icon to About This Mac and click it. Then click on the System Report button. It will bring up an extensive report. Under the Hardware section, at the bottom, click on USB to show everything that is connected via USB and hopefully, you will see your disk. There may be a lot of data, so you have to look for it. If you do see your drive, then you know that the computer recognizes it and it should be visible.

One problem with connecting certain drives and devices via USB hubs is that too much power may be drawn if the USB hub is not a powered hub. I've found that using powered hubs solves a lot of problems. My last thought is if the disk is still not showing up when directly connected to the computer, I would then try using a different USB port. It could be that one of your ports is defective. Good luck.