Bsod - kernel_data_inpage_error

Hello :) I started gaming again on my PC after a break. Unfortunately, I get BSOD error Kernel_data_inpage_error

Tech Support Guy System Info Utility version 1.0.0.2
OS Version: Microsoft Windows 8.1 Pro, 64 bit
Processor: Intel(R) Core(TM) i5 CPU 750 @ 2.67GHz, Intel64 Family 6 Model 30 Stepping 5
Processor Count: 4
RAM: 8158 Mb
Graphics Card: AMD Radeon HD 5800 Series, 1024 Mb
Hard Drives: C: Total - 61054 MB, Free - 13528 MB; D: Total - 715300 MB, Free - 186806 MB;
Motherboard: ASUSTeK Computer INC., P7H55-V
Antivirus: Windows Defender, Disabled

I tried to do chkdsk c: /r on cmd.exe but I hit "y" to perform checkdisk on restart and is not working.

I tried to downgrade from win 8.1 to 7 but was unlucky. I couldn't format C: and the installation failed.

Can you please help me.
I 'd be grateful :)

Irene