Also having this problem with a Latitude E7450 on company laptop (Service Tag:  DM9YN32) that belongs to one of our Exec VP's.   We've actually had several problems with this laptop direct from factory which required us to replace both the motherboard & the WLAN.
As of now, this laptop currently has the latest  video driver and hub drivers installed for this mode (which I listed below)  This laptop is docked with two external monitors running both in DVI to the port replicator. Our team has replaced the port replicator, tried different monitors, tried different monitor cables (IE: both DVI & VGA), and also replaced the power adapter.    Historically the monitors would flicker back and forth on and off.  If we disconnect one monitor then it works fine.  But running duel monitors the problem comes back with one or both monitors flickering on and off.  After I installed the HUB firmware update, the problem appeared to have gone away for a couple hours but then came back where the primary monitor shut off for a few seconds.  
NOTE:  I realize that there is also a NVIDIA driver for this model of laptop but in this case this driver is not compatible with his laptop so obviously the nvidia GPU chipset is not on this laptop.
Drivers currently installed as of 4/9/2015.

Intel HD, HD 4200/4400/4600/5000/5100/5200/5300/5500 Graphics Driver

I need to retract one statement on my previous post.  It was brought to my attention that even with only 1 monitor plugged in, the behavior as discussed in this post continues.  So it does not matter if we have 1 or two monitors plugged in (the monitor will randomly blackout) in intervals.  

Hi, thanks for the posts.

Mlinh – Sounds like you could have a bad, possibly corrupt driver installed. I suggest rolling back to the previous driver installed, hopefully you will regain video. Check out this guide from Microsoft on rolling back drivers http://windows.microsoft.com/en-us/windows/restore-driver-previous-version#1TC=windows-7

If updating he driver again be sure to do so from the Dell Drivers & Downloads Website for Dell certified drivers.

Kirk Eld – Did the issues on your system also start around the time of the BIOS or driver updates you mentioned? If so I suggest initially testing the same steps recommended above. If not, was any new hardware added to your configuration recently? Removing anything that was added to the systems configuration recently or around the time these issues first started would be a great help in troubleshooting the cause.

In case the Video and BIOS are not already updated to the latest I would suggest updating, Please let us know how it goes!

Thanks,

Updated an E7450 with flickering screens on the docking station to Bios A04, Video driver A16 and Synaptics Hub A01. Without the video driver the flickering increased. Not sure yet if the video driver improved the situation. To be on the safe side, I ran the hub update again on the users dockingstation.

Any tips on this issue

Random blackouts on external monitors with Intel HD 5500 Graphics in a Latitude E7450 is also the topic of my recent (as of yet unresolved) post http://en.community.dell.com/support-forums/laptop/f/3519/p/19635311/20778201#20778201 but in my case it involves Display Ports. I suspect one or more driver bugs which may have been addressed in Intel's latest driver release, which has not yet been made avaliable for Dell laptops with the Intel HD 5500 graphics hardware.

No luck, the random blackouts remain

I am experiencing similar problems getting the display to show on the docking station... has anyone figured this out?

I am running a Dell E7450 laptop with Intel 5500 integrated HD Graphics.  My external monitor is an HP LP3065 running at 2560x1600.  This monitor only has DVI inputs so I connected it to the laptop's docking station through the Displayport with the StarTech DisplayPort to DVI Dual Link Active Video Adapter Converter (DP2DVID2).  My external display would flicker randomly - sometimes every few seconds, and sometimes only every 10-15 minutes.  After hours of trial and error, I think the issue was finally solved by going to the Intel HD Graphics Control Panel, select "Power" options, then under "Graphics Power Plans" select "MAXIMUM PERFORMANCE".  Previously I was using the "Balanced Mode" setting and I think every time the GPU automatically switched modes it was creating a glitch that would cause my monitor to flicker.  Another note - my BIOS and all drivers are up-to-date.  I hope this helps somebody else save hours of frustration.

Hi,

Did you find the solution to this issue?

Kinds regards,

Spam03

According to Dell the steps are:

Download latest bios, video and synaptics hub firmware:

www.dell.com/.../drivers

- Update the bios to latest
- Update video driver to latest
- Update the Synaptics Hub firmware (while the laptop is on docking station)

Found this to be working for most of our laptops