Okay, there's a few things that might be going on here. So, let's if we can get you fixed up.
First of all, as far as I know, you should never link your weapon/blad to your quick bar. Instead, you should equip it, by dragging it from your invetory to the correct slot on your character screen.
Once its there, you never have to deal with it again.
What may be happening is that you are losing your attack ability buttons somehow. Try this. First of all, look to the right of your quickbar and you will see up and down arrows that will move you up and down through a number of quickbars. Click these up and down and see if you have accidentally switched to a different blank quickbar.
If that's not the case, then try re-adding your attack abilities to your quickbar. Up at the top of your screen, you will see some icons. One is for a list of your abilities and powers. Find the ones that you are missing and then drag them down to spots on your quickbar.
The last thing that I can think of that may be happening is that maybe your blade is breaking? (although it hasn't happened to be before, maybe its possible?) Try this to be sure. Go to any merchant and right-click them. At the bottom of their window, you will see REPAIR. Click that and see if your equipment needs repairing.
Oh, and you can also click on the BUY BACK button at the bottom of the merchant window. Maybe you accidentally sold them? If so, you can get them back that way.
I hope this info helps you get back in the game and killing alien monsters again!