Stuck on Grey Screen During Startup
It is already become usual when new OS update finally break defective GPUs.

You didn't state what exact model of early 2011 you have but if it is 15" or 17" it just may be it since Radeon HD in those models tend to break.

If yours MBP is indeed with Radeon GPU try to use towel method i.e. wrap it into bath towel (dry of course) after startup and let it sit and become really hot. Try to restart after it. If it working you might try this approach