As others have stated, first check with the POS software company to see if they have a update for Windows 10. The software is probably not compatible with Windows 10. If they do not then your best course of action would be to go back to Windows 8. If you did the upgrade and it was recent you can press (Windows key +i) go into Backups and Recovery and there should be an option to revert back to your Windows 8 install.