What part of my computer broke？

[yinchi2003]

Yesterday my pc is still ok.But today when I start it,it had a sound like knocking door.And it auto off.A few sec later it repeat on and off.I already try another ram and put another graphic card. But it still same.I couldn't smell anything and don't have any parts got burning.How do I identify which part.
Sorry for my bad English

 

[1LiquidPC]

Not sure of the "knocking door" sound, but do you have another power supply to test? If nothing changed before this started, it's a possible cause based on symptoms. Do you have full system specs you could share?

 

[yinchi2003]

ok

 

[yinchi2003]

No I don't have another PSU.
Graphic card:gt 1030 2GB
CPU:i3-2120
PSU:GX Bronze 400W
RAM:2 x 4GB DDR3
If I missed something u can tell me again

 

[1LiquidPC]

What brand and model is the GX 400W?

 

[SkyNetRising]

when I start it,it had a sound like knocking door.

"Knocking door" sound? Could be dead HDD.

 

[yinchi2003]

How can I reply u guys message on mobile phone？I cant find any botton.My PSU is cooler master.

 

[jaslion]

How can I reply u guys message on mobile phone？I cant find any botton.My PSU is cooler master.

Is the text on the cx green? If so you have one of the bad cx psu's. The knocking sound can be a cap bursting or something else in the psu. Which wouldn't be too suprising since if it's the one with the green text since those are known to do so.

 

[yinchi2003]

No..Mine is GX Bronze 400W with red text.How can I check inside the psu.