thunderbolt sets mac asleep

I got a Mac Book Pro (13-inch late 2011, OS X Yosemite 10.10.5, all available Updates downloated) and Thunderbolt Display (late 2001).

My Mac never gets into sleep modus when it is at the charging cable and I have no Password after fallen asleep.

When I put the Mac at der Thunderbolt Display (also with charging cable) after a few minutes not working at the Mac, the Mac falls asleep and the microsoft offices programs get closed, so that I have to log in like I start my Mac new.

Also when I let music play, after a few minutes the Mac shuts down, the Displays gets black and the screen protector isn´t working anymore. Then I also have to log in new.

I tried everything in the settings, there is no help in the internet and the phone support form apple also could´t help me.

I hope you can, because I am really desperate. i don´t use my Thunderbolt anymore and for that I was way too expensive. THX a lot