Ah! Seems like I've found the setting in KVirc files that tells KVirc where to position main window!
Close your Kvirc, go to your Settings\config\ directory and open
main.kvc in a text editor.
(If you don't know where exactly your local KVirc settings folder is, run in KVirc
/echo $file.localdir)
Find the line like this one (search
rectFrameGeometry keyword):
rectFrameGeometry=10,99,498,286
it is in the format X, Y, Width, Height (coordinates start in the Upper-Left corner of a screen)
And see if it has reasonable values. If not, edit them accordingly, save. Open KVirc!