Frozen at startup screen intermittenly

I have a MBP that is in great shape.

Its great. Its fast most the time.

But about every 3-4 times I open it, it freezes upon starting up.

Sometimes it makes a sound when I unplug it from the power cord (like the sound of a disk booting up) and sometimes it doesn't.

Sometimes, it acts like it's rebooting the entire computer even though it should just be waking up, but sometimes it doesn't.

Sometimes it shows the progress bar like it's starting up, and sometimes it doesn't....

But regardless of those sometimes it does and sometimes it doesn't, what happens next always happens...

- First it lets me log in with my password,

- Then the screen changes for a moment, only to bring me back to a different looking password screen....BUT I CANNOT MOVE MY MOUSE OR USE THE KEYBOARD!?

- Then after about 30-60 seconds, the screen goes black and it goes to sleep,

- So I touch a key to awaken it, and it is still frozen for 30-60 seconds before going to sleep again,

- I awaken it and it'll sit there frozen for another 1-2 minutes,

- Without changing anything, at some point in the next few minutes I can finally use the keyboard and type in my password...

- And sometimes, it will be slow as molasses for 30 minutes after letting me...and sometimes it's just fine.

Any thoughts on what's wrong or how I fix this?

PS. I feel like I have done every test, have reinstalled everything and reloaded each app again. Nothing helps. Any ideas would be great.

It has done this will Mt Lion, Mavericks, Yosemite - nothing changes it.