Digital cable providers use digital converter boxes to provide their customers with numerous features that cannot be offered over traditional analog cable service. These features include DVR recording, on-screen channel guides, program reminders, video-on-demand services and many others -- all of which require a digital cable box. A common feature of cable boxes are the LED status indicator lights that show when the cable box is on and indicates the health of the box. If one of these LEDs is red or another color rather than green, you can narrow down and diagnose the problem in a few simple steps.
Reset the cable box by unplugging its power cord for 30 seconds and plugging it back in. Give the box time to fully reboot and give an additional 5 to 10 minutes to see if the LED turns green. Some cable box LEDs simply indicate whether the box is powered on, in which case they typically turn green. Some indicate whether it is in standby or power-save mode, in which case it may be yellow, red, or another color. If the LED is still red, however, some additional troubleshooting is required.
Check the coaxial cable that attaches your wall cable jack to the coaxial input on the cable box. If the cable is loose, dirty, or damaged, the cable box may be incapable of receiving authorization signals from your cable provider, which is one common cause for an LED not going green. Clean any cables that are dirty and replace any cables that appear damaged beyond repair. Tighten the coaxial cable by hand both at the wall outlet and on the cable box, and reset the box again in the manner described in step 1. If the LED light now turns green, most likely the box was simply not receiving service over the coaxial connection and now the box should act normally.
Contact your cable provider and inquire as to the purpose of the LED. In some cases, a red LED may not necessarily indicate a problem with the box, but may indicate that the box is in good health and behaving normally. If not, have them troubleshoot the red LED and replace the cable box if necessary.