If the light on the magnetic strip reader is flashing regularly this means that you may have a hardware failure. Different POS machines use different card readers, sometimes manufacturers change their readers from year to year. begin by trying to identify the MSR you are using and then refer to the hardware manual for trouble shooting tips.
Each time the Card Reader is powered itwill go through a system check and verify that all of its hardware is functioning properly. If the Card Reader finds a problem it will sound a series of error beeps and/or LED changes. The following is a list of error beeps and LED changes and their meaning.
Classic Line SLOW BLINKING ORANGE LED CPU ERROR LOW,MED,HIGH BEEP PROM ERROR FAST BLINKING ORANGE LED RAM ERROR LOW FOLLOWED BY 2 HIGHER BEEPS EEPROM ERROR
Value Line FLASHING RED LED, 3 BEEPS CPU ERROR FLASHING RED LED, 4 BEEPS MEMORY ERROR FLASHING RED LED CONTINUOUSLY DECODE CIRCUIT ERROR
There is a manual attached here, but you should check the hardware manufacturer site for their most current guides.