AMD RADEON R9 380 2GB GAMING STARTED TO RUN AT 300 MHz

Computer Type: Desktop

GPU: AMD Radeon (TM) R9 380 Series 2GB Gaming NO OVERCLOCK

CPU: AMD FX(tm)-8300 Eight-Core Processor NO OVERCLOCK

Motherboard: MSI 970 GAMING

RAM: DDR3 16GB PC 1600 CL9 G.Skill KIT (4x4GB) 16GBXL RipjawsX

PSU: Cooler Master G750M A/EU 750W 80 Plus Power Supply

Operating System & Version: Windows 10 64 bit

GPU Drivers: Crimson ReLive 17.4.1

Description of Problem:My graphic card started to run at 300MHz . Why it happend i defintly dont know. Please, help me.