Synaptic Package Manager: can't close it

I'm rather new to Linux and to MEPIS. [I believe I'm now running SM 3.3.1-1.]

I've used Synaptic Package Manager a number of times and had no troubles with it. But I recently did something to it either while it was idle or while it was running and perhaps whatever I did accounts for the new problem. [As I recall, a few weeks ago I changed something in the sources it checks for new packages.] Now I can't close Synaptic Package Manager.

I run it as I did in the near past. With my dial-in connection, it takes some time to download all sorts of things so I can later review what I want to upgrade/update. But then, after the downloading ends, all I see is every pane either blank or dimmed. I only see a watch where the mouse pointer should be.

I try everything to shut it down but nothing closes it. What's wrong and how is this fixed?

Thanks,

Stan