Hello, sadyka, Welcome to the forum,
Let's see if we can bring a solution to your case
I am John,
And first, I want you to download these 2 programs linked below,GPU-ZSpeed Fan
Please download the benchmark program UNIGINE Valley, linked below,Unigine Valley
After you set up Unigine Valley, run the program by double clicking, Then select DX10, it is your GPU's dx version. Set, the rest of the settings to maximum. Then click run. Please uncheck fullscreen.
NOTE: I suggest you to keep an aggresive fan profile during Unigine tests, because we dont want overheating get in our way. Set your fan around 55-60% so that the card can stay cool during our tests.
Your problem may because of a defected PSU, since a 550w PSU should power a gts250 without any problem.
Ok, while you are running Unigine with fullscreen unchecked, please run the two monitoring programs you downloaded.
And send me screenshots from Speedfan, regarding voltages on 12V rail and 5V rail.
Also, from GPU-Z send me readings on the Sensors tab, the very middle one of the three tabs above.
Especially note the min. and max values on the VDDC
and VDDC Current
VDDC current box is right below VDDC box, so you cant miss it. scroll down the bar if you need to, because we dont have to see the temps above really
That's it take care,
+1 if it helps,