Try Different USB Port:

Simple first test. USB ports can fail. Try different ports, preferably on the back of desktop computers.

Test on Another Computer:

Determines if mouse or computer is the problem. Working elsewhere means computer issue. Not working means mouse issue.

For Wireless Mouse:

Check batteries first—most common cause. Re-pair the USB receiver. Keep receiver close to mouse to avoid interference.

For Bluetooth Mouse:

Toggle Bluetooth off and on. Remove mouse and pair again. Check if Bluetooth adapter is working.

Update Mouse Driver:

Device Manager > Mice and pointing devices > Update driver. Or uninstall and restart for automatic reinstallation.

Clean the Mouse:

Optical sensors get dusty. Clean the bottom lens carefully. Ensure the surface you're using works with the sensor type.

Conclusion:

Port changes and batteries solve most issues. Wireless mice are more prone to problems than wired ones.