Question Why does Windows sometimes not detect my USB speakers ?

Update your post to include full system hardware specs and OS information.

Double check that the USB connection is fully and firmly in place.

Try the speakers on another known working computer.

Try other known working working speaker on your computer.

Determine if the detection failure follows the speakers or stays with your computer.

Could be a problem USB plug, port, or even the cable itself. Intermittent problems are more difficult to solve.