First, make sure you have the MOST recent BIOS version for your motherboard installed. Compare your current version against the latest version available on your motherboard's product page. If there is a newer version, update, then try the card again.
Second, after doing so, if necessary, and WITH the new card installed, try doing the following.
Power off the unit, switch the PSU off and unplug the PSU cord from either the wall or the power supply.
Remove the motherboard CMOS battery for five minutes. During that five minutes, press the power button on the case for 30 seconds. After the five minutes is up, reinstall the CMOS battery making sure to insert it with the correct side up just as it came out.
Now, plug the power supply cable back in, switch the PSU back on and power up the system. It should display the POST screen and the options to enter CMOS/BIOS setup. Enter the bios setup program and reconfigure the boot settings for either the Windows boot manager or for legacy systems, the drive your OS is installed on if necessary.
Save settings and exit. If the system will POST and boot then you can move forward from there including going back into the bios and configuring any other custom settings you may need to configure such as Memory XMP profile settings, custom fan profile settings or other specific settings you may have previously had configured that were wiped out by resetting the CMOS.
If that will not resolve your issue then we need to start looking at what the EXACT model of your "500w PSU" is, and where you obtained this graphics card from. Did you purchase it new or used?
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