If you are using the version 5 sequencer software, then please try the Total Tester program (Start Menu -> All Programs -> ACM Instruments version 5 -> Total Tester). If the Total Tester cannot communicate with the instrument it can suggest possible causes with its help pages.
These help pages are available on line here and may also be helpful to other automated instruments besides version 5.
If you are using a USB connection to the instrument then try the USB reset tool that can solve some driver issues.
For additional help with communication problems see Using a USB to serial Converter and Windows Vista, 7 and 8 USB Drivers which also includes video demonstrations on how to update your USB drivers, how to reset your USB drivers and how to use our FTDI USB Reset Tool.
Please contact ACM Instruments if you need further assistance.