please help me! my pc hangs seriously with buzzing speaker and monitor turns off

Mar 25, 2018
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I am having a serious problem. Today I turned on my pc normally and started working after some time my pc became very slow so I restarted my pc manually and the pc started fine and I started my work again. Suddenly my pc hanged the monitor turned off, the keyboard"s numlock led turned off and a noise was coming from the speaker but the cpu was running. I tried to restart my pc but couldn't not because pc was seriously hanged then I unplugged my pc from the socket and started my pc again it ran fine and again hanged but this time the monitor was on error showed " inaccessible boot device". I thought the display driver was causing the problem. So I started a clean windows setup and after 10-12 minutes the same thing happened (I already formatted the system drive) then restarted my pc I saw the the hdd was gone I again restarted my pc, first and second time it turned off itself but third time it started. I entered the bios and saw the hdd was present. Cpu snd system temp was normal i saw in the bios. Please help me.

My pc spec:
I5 6500
Gigabyte b150m d3h ddr4
8gb team elite 4*2
Lg CRT monitor
China casing and psu I got with the casing.

Please help me.