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#11
Just a suggestion..... but if you want to return to that lovely blue dual boot screen then you'll need to Fix the MBR... I use Macrium Reflect in which you can create a Win PE rescue USB drive. Once you create that and boot into it the menu on the left has 'Fix Master Boot Record' option.
Macrium Reflect Free
Create a Windows PE Rescue Environment
Works for me with dual booting from 2 different partitions using windows 7 and 8.1 when I get the occasional black and white DOS looking dual boot choice screen.... just insert the Macrium Win PE thumb drive and fix MBR.... takes 60 seconds.
As for exactly what causes it I'll leave to those who can explain why it happens.