Serious issue with macbook pro and thunderbolt display

Hi,

I own an early 2011 macbook pro 15" and it's hooked up to a 27" thunderbolt display. Since couple of days ago I started having this strange but somewhat serious problem as explained below.

As soon as I'm done using the macbook, I tend to put the system to sleep from the apple icon, top left corner. All is goo here. As soon as I try to wake it up, by pressing the spacebar on the bluetooth keyboard, I can see that the system wakes up (as the white light is now solid and not fading in and out anymore) but both macbook screen and thunderbolt display are completely black. After few seconds like this, a white screen is shown only on the macbook screen and the whole system restarts, prompting that there was an error and the system had to restart.

When the laptop restarts, the thunderbolt display does not turn on - even the peripherals hooked to the display stay off until I unplug the thunderbolt connection and put it back in. This is quite frustrating as 1) the whole system restarts losing all open windows, browser tabs, etc and 2) there clearly seems to be a problem.

System has 2.2 GHz Intel Core i7 processor with 16GB RAM and OSX v. 10.10.3.

I would greatly appreciate if someone can give me some tips on how to solve this or possible solutions to this issue.

Many thanks!

Paul