MacBook Pro Retina hangs on startup when connected to Thunderbolt Display

Question

I have a MacBook Pro Retina and it's basically almost always connected to my Thunderbolt Display. Each time I start it up, I open the MacBook just slightly and press the power button - and almost instantly the MacBook goes ontop the startup Login screen and at this point is where I close the MacBook and login through the Thunderbolt Display.
Since last night for the very first time - My MacBook Pro hangs on a white screen and takes a long time before going to the Login screen. I've tried to swith the Thunderbolt Display off from the mains - I've also tried to boot up my MacBook on it's own without it being connected to the Thunderbold Display and all is fine (it almost immediatelly shows the Apple logo and then staright onto the Login screen then BUT as explained, as soon as the MacBook is connected to the Thunderbolt Display and I power it up - it hangs on a white screen for about 30 - 60 seconds before it goes to the login screen!
I have no idea how from one day to the next this could happen? Perhaps it's some Apple updates I've made recently which I cant really recall because I usually just update software when required to do so.
Hoping anyone can help.

Answer 1

Hello FunkTunes,
I recommend this section of the article Apple computers: Troubleshooting issues with video on internal or external displays found here http://support.apple.com/kb/ht1573.
Check connections
When using an external display be sure to check the following:
If you're using an Apple notebook, confirm the AC power cable or adapter is securely connected to the computer and the cable providing power to the display is also secure. It is always good to have your notebook connected to AC power when an external display is in use.
Confirm display adapters are fully seated in their respective connections and that they are supported models and for the computer and display. Refer to these articles to assist you with adapter compatibility and further configuration information:
Monitor and Display Adapter Table
About Mini DisplayPort to HDMI adapters
Apple Mini DisplayPort adapters: Frequently asked questions (FAQ)
Thunderbolt ports and displays: Frequently asked questions (FAQ)
Remove all display cable extenders, KVM switches, or other like devices and retest to determine if the issue is resolved.
Try unplugging the video adapter or cable and then plug it back in.
If more than one video adapter is in use (or "daisy-chained"), troubleshoot by using only one adapter.
Example: A mini DisplayPort to DVI adapter connected to a DVI to HDMI adapter is an unsupported configuration because there is a series of adapters in use.
If available, try using a different display and or adapter (or use a different connector by using DVI instead of VGA, for instance).
Reset the system
You can reset the Mac's parameter RAM and SMC.Reset the resolutionStart by resetting the Mac's parameter RAM. If the display does not come up, was previously set to an unsupported resolution, and still results in no video:
Start up in Safe Mode.
From the Apple () menu, choose System Preferences.
Choose Displays from the View menu to open the preferences pane.
Select any resolution and refresh rate that your display supports.
Restart your computer.
All the best,
Sterling