[Unable to use Selection Tools]

THANK YOU!!! You are a genius!! And I feel like a real dummy now - I knew it was something really simple - which was why I waited so long to post a question!!but I am so appreciative of the answer!!

[Unable to use Selection Tools]

Some of my selection tools are not working. I have relaunched the Affinity Photo software, I have rebooted my laptop, MANY times - but some of the selection tools will work. If I activate (for example) the selection Brush tool, it APPEARS to be working - i.e. the mouse turns into the round selection brush but when I click / drag, nothing is selected. The same thing happens if I try to use the rectangular or spherical selection tool - it looks like it SHOULD work, but when I click and drag - nothing happens -  the selection pen tool does work, but is not always the best option. I thought it might be my mouse, but the mouse works well enough for painting, erasing etc.

Is there something I am doing wrong? I am not new to photo editing software and the selection tools did work up until a couple weeks ago . . . I have not changed any settings or preferences but not having the use of all of the select tools is a real drag!! Any help would be appreciated!