MacBook Pro trackpad has stopped working

I was working on my MacBook Pro earlier without problem, then put it down to take a phone call. When I took the laptop again, it is like the trackpad has partly stopped working. I can move the cursor around, but I cannot click on anything, and it doesn't appear to register any tap or click. I can occasionally get a two finger click, but this is it.

Has anyone experienced this, and is there a quick fix for it? I have rebooted the laptop four times now, to no avail. Please help... Interestingly, I also often work on this laptop with a external trackpad, like I do on my desktop, and this too seem to have lost the ability to click and select.