As @GiantHunger stated, we'll need your full PC specs to help start the trouble-shooting.
When you say, "my 2nd hand graphics card", can you go into details on what you mean. Did you buy it off e-bay, Amazon, etc. or from a friend? Did you verify the card worked prior to purchasing, as depending on the time of purchase last year, there was a lot of scamming going on with people selling defective cards as no one could get a GPU with the market shortage. Hey, people were selling just the box for 30 series cards for $600+ as people weren't reading the description and just saw a post for a 30 series card on e-bay.
Have you tried another HDMI cable or another cable input for your GPU to monitor connection?
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can you give the information of your pc spec?
Asrock B450M Steel Legends
T Force Delta 2x8gb 3200mhz
Ryzen 3 3300X
Tecware Forge M2
Western Green 240gb ssd.
I bought it from fb marketplace and they send me proof of working. I didn't test it when I already have the gpu 'cause the card is not compatible to my old pc, that's why I suspected the card is dead but when it does have a post last day I think the gpu is not dead. Yesterday I tried to go to a technician but he said I need only to clean the gold pins with eraser just like cleaning the gold pins of ram, I did clean the pins and repasting the card but same result. I didn't try another hdmi cable or other input on my monitor, I only have one hdmi cable. Thank you for your response, appreciated.