hi to everybody 
I have 2 external usb hdds plugged to my Acer/Mabox desktop. Since today I can’t boot anymore… the pc gets stuck at the point with the Acer logo in the screen centre and the “Press Del to enter the Bios Setup Menu or F12 to display the Boot Menu” (or something worded slightly differently). Obviously at this point if I hit Del, F12 or anything else nothing happens, I can only switch the pc manually, unplug the disks and start again (and now it boots effortlessly…).
I’m pretty sure this didn’t happen when I had only 1 hd plugged (in a usb 3 plug), yesterday I added another, plugged in a usb 2 and today this happened (removing the usb 2 plugged hd didn’t solve the issue…).
Now, sure I can plug the disks only when the pc is already on and running, but it would be much easier to have them always there.
Any idea on how to sort this?
Thanks! 
I did find something. Somewhere (guess on Reddit but haven’t saved it, and can’t find it again) I found someone having a broadly similar problem and he fixed it deleting a hidden .Trash-0 folder. I looked in the usb 3 connected hd (it’s an older hd, I was using it with the previous machine with Manjaro Openbox) and there was indeed .Trash-1000 folder. I deleted it, and this has apparently fixed the issue, but ONLY if this is the only external hd. If I connect the other, a brand new one, to a usb 2 plug (because on this small Acer desktop I’ve run out of usb 3 in the back…) it stops the boot 
The “old” hd is ext4, the new one exfat. I’ve installed exfatprogs as GParted was telling me it was missing. I’ve searched for a hidden .Trash folders but there weren’t any. The pc keeps freezing during booting.
I’ve formatted the hd to ext4. It hasn’t helped.
I guess unplugging the hd every time I switch the pc off and then unplugging after the next boot isn’t too bad… but still, if possible, I’d prefer a permanent fix.
Both hd get their power from the usb plug.
Hi @Finrod
Did you try simply setting your main hard drive (the one with Mabox) as the first boot option on your BIOS? 
thanks! I’m pretty sure I did that already 
but sure I’ll check (not now and not in a few days as in a couple of hours I’ll wrap everything and fly to my one week holiday). However something similar happened too in my previous machine with Manjaro Openbox, there was one and only one external hd (the one I used for backups, i.e. not one I needed plugged all the time) that froze the boot in (apparently) the same way…