"So it should be on?"  As long as there's HDD activity, it should be on.  It will flicker accordingly.
Gentleman.  This is probably going to get me laughed at but I had a I/O panel symble show up tonight after a complete tair down and paint .  I have a mid tower 9020 built in 2014 , after the tair down I powered it up with only the tower plugged in and got a flashing light on the front panel that looked like a can. Ya a can, now I should have plugged in the monitor keyboard and all but I didn't I shut it off.   Well after a few hours looking on the internet I came back here to ask a stupid Question. Can anyone tell me what the can looking light is supposed to be so I can carry on. Thank you Bob    
Dell 9920 front panel system