Sometimes, if the scanner has been bumped or accidentally unplugged it can reset itself.
There are a number of things you can try to trouble shoot:
1. Turn the scanner off and on again
2. Check that the scanner is plugged in firmly at both ends
3. Scan a barcode and take a note of the lights on the top i.e Are they flashing? Are they blue or white?
4. Scan a barcode and check to see if the scanner beeps
5. Open notepad and scan a barcode, if the scanned barcode displays as a number then the scanner is in USB mode - See the Scanner Serial Mode article for a guide to resetting the scanner to serial mode
6. If the scanned barcode doesn't display, then the scanner is already in serial mode and you may need to scan the Set minimum barcode length codes attached to this article
7. Check Devices and Printers through Windows and make sure that VisitorRego is looking for the same scanner com port
8. Restart VisitorRego and test