Why does my computer turn on but show a black screen?

Because you do not see the BIOS or manufacturer logo, this is probably not a Windows 10 problem. The computer is failing before Windows starts, or no video signal is reaching the monitor. Reinstalling or resetting Windows will not help at this stage.

Try a minimal startup:

1. Turn the computer off and unplug its power cable.
2. Hold the power button for about 20 seconds.
3. Disconnect all USB devices, external drives and unnecessary accessories.
4. Connect only the monitor, keyboard and power cable, then try starting it again.

For a desktop computer, check where the monitor cable is connected. If the PC has a separate graphics card, the cable normally needs to be connected to that card rather than the video ports on the motherboard.

Since you have already reseated the RAM, test one memory module at a time in the slot recommended by the motherboard manual. Try each module separately. A fan can still spin even when the computer cannot complete its startup hardware check.

Next, check the graphics card:

1. Turn off and unplug the PC.
2. Reseat the graphics card and check its power connectors.
3. If the processor supports integrated graphics, remove the graphics card and test the motherboard video output.

Look for diagnostic lights or a two-digit code on the motherboard, and listen for beep codes. The motherboard manual explains what each light or code means. You can also clear the CMOS using the method in that manual.

If there is still no BIOS display with only one RAM module and the minimum hardware connected, the likely causes are the power supply, graphics card, motherboard or processor. A power supply can run the fans while still failing to provide stable power to the other components. Test with known-good parts if available, or have a repair shop perform the hardware checks. Never open the power supply itself.

Because there is no BIOS logo, Windows has not started yet; this is a firmware, graphics, power, or hardware-initialization problem. Disconnect storage accessories and all USB devices except a wired keyboard. Shut down, remove power, hold the power button for about 15 seconds, reconnect one monitor directly, and try again. If the processor supports integrated graphics, connect the display to the motherboard after removing or disabling the discrete GPU; otherwise reseat the GPU and verify PCIe power connectors. Test one RAM module at a time in the motherboard-recommended slot. Check the board’s diagnostic LEDs or beep code and consult its manual for the indicated component. Reset UEFI settings using the manufacturer’s documented CMOS procedure only after recording custom settings. If a firmware logo appears, continue with Microsoft’s Windows blank-screen steps. If no logo appears with minimal hardware, Windows repair commands cannot help; the failing component needs hardware diagnostics or service.

Test video output from the motherboard instead of the GPU.

If you have a dedicated graphics card, plug the monitor into the motherboard's video output instead (near the CPU I/O ports) rather than the GPU.

If you get a display this way, your GPU is the problem.