CPU permanenttly works on half of clock

Hello everyone!

I encountered with problem and I have absolutely no idea how to resolve it.

I have an iMac mid 2011 27" with core i5-2400 (3100MHz) radeon 6970-1gb HDD 1TB .

https://s31.postimg.org/jnregi8ob/Screen...

My HDD had broken, so i decided to install SDD instead of it. So I replaced old hard disk and put ssd Crucial MX200 500Gb instead. I installed Mac OS 10.7 from scratch using embedded recovery system, and after what updated to 10.11.5.

Everything was fine until I decided pass some benchmarks. And all benchmarks show that cpu results only a half of expected. E.g Cinebench R15

https://s31.postimg.org/z28vmj2bf/Screen...

I tried to figure out what the problem and install Intel Power Gadget utility.

It reveals next - CPU frequency does not rise higher than 1600MHz even in 100% cpu load tasks. It freeze on 1.60GHz a not move even a bit. The line on the graph is absolutely flat!

https://s32.postimg.org/npa8t9bhx/Screen...

And there are no CPU overheat as all! Temperature not raises more than 50C degrees.

And GPU also work at ~20% of it power according to benchmarks (two times less points than ge-force 620m has).

I have no idea how to resolve this issue. Please share your experience in such cases