Can't drag!

I was working on my iMac last night, with the new OS, and I don't know what I did exactly but it seems I hit some key or key combo, and now I can't drag anything. Can't drag icons on the desktop, can't drag items out of a finder window, nothin.

I can highlight and select and open things, but no dragging. I'm completely stumped and don't know where to start.

I use two input devices, a mouse and an Intuos tablet.

Any advice would help.

Honestly, I have never seen this, but as a first step have you tried doing a cold reboot? Power down, unplug your iMac from the wall and wait a minute or two then restart.
That often fixes or unfreezes strange problems.

Yep, I should have restarted last night, but just shut down meaning to try it later. I'll see tonight if it's behaving.

After a restart everything's fine! Thanks for your response, Razormac.

You are welcome.