Hi Wally,
If you 'lose' the ability to resize windows for any reason, look at the top-right corner of your main PixInsight window.
Below the icons that control the overall PixInsight window, you should see four icons:
The first (looking like a 'minus' symbol, "-") is called "Iconise" in the Tooltip that appears if you hover over the icon.
The second looks like an upwards-pointing triangle, topped by a hprizontal line, and the ToolTip states that this is the "Shade" icon.
The third is a small square box, called "Normalize".
The fourth is a small black cross, "X", called "Close".
If you click the third icon, "Normalize", things should - hopefully - return to normal.