Both times when I fiddled with the sticking key a bit and to get it unstuck, the problem of the keyboard disconnecting (despite the number pad working) went away - no more taking the batteries out and putting them back in every time I stopped using the keyboard for a few minutes.
Thank you!!
I hope the previously 10+ pages are all responding to this post. For reasons none of us can understand some of the keys get stuck. My was the 'PrtScn' key. Lots of pressing and some careful cleaning has seemingly free'ed the key. But it does feel as though it's going to get stuck again.
Open notepad and check every single key.