I have exactly the same problem so would be good to find out what caues this and how it can be cleared.

Internet searches suggests that its a diagnostic mode  and that it needs dell to reset.

There are many varied fixes to that problem.

 

Usually, Fn + X resets it.

 

Sometimes, going into the System BIOS setting and resetting to the defaults can fix it (Alt + f)

 

Sometimes a motherboard change will fix it.

 

Sometimes a BIOS upgrade will fix it.

 

Unfortunately, sometimes none of the above will fix it.

 

if a system is stuck in manufacturing mode, it might suggest a motherboard failure