If you boot up and Windows (or Linux) is active and you (still) see this LED flashing, it could be an indication that the Intel Management Engine (ME) is in a bad state. If this is NOT the case, you can ignore the remainder of this message.
If the ME appears to be in a bad state, go into BIOS Setup and, from the main scene, scroll down and select Additional System Information. In this scene, scroll down to the very bottom. There should be an entry near the bottom that provides the version number for the ME firmware. If this is displaying as 0.0.0.0 or is blank (i.e. not providing a version number), then this is an indication that the ME is not operating. The typical reason for the ME not operating is because a bad BIOS update occurred and it deleted/corrupted the ME firmware.
You can attempt to recover from this state by reinstalling the latest BIOS using the BIOS Recovery method. For information on BIOS Update processes, consult Intel Desktop Boards BIOS Update Instructions and, for this case, Intel Desktop Boards Recovery BIOS Update Instructions.
To help you better, here are my step-by-step instructions for BIOS Recovery:
Hope this helps,
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Currently this desktop tower is booting up and seems to be functioning normally without any on screen alerts.
I was concerned that the continuous flashing red 'M' LED was not normal. I notice this flashing LED before shutting down to install an additional HD.
I am currently running Win7 and about to upgrade to Win10.