I'm building a PC for my younger sister using an Intel Core i5-10400F, ASRock B560M-C motherboard, 16GB of DDR4-3600 RAM, a 500GB Colorful SSD, an EVGA GTX 1660 Super, and a Montech Beta 2 550W power supply. Some parts were originally used, but I replaced them with brand-new components after the system failed to boot, and the replacement parts produce the same behavior.
When I power it on, the motherboard's DRAM light comes on first and then turns off. A few seconds later, the BOOT and VGA lights come on together; sometimes the BOOT light flickers before both turn off. The TV detects that an HDMI device has connected, but there is no picture at all. The graphics card's 8-pin power cable is connected. I've also tried one RAM stick at a time in both the A2 and B2 slots and have cleared the CMOS. What should I check next?
3 Answers
Check the display side carefully: use a different HDMI cable or monitor input, try another output on the graphics card, and confirm the TV is manually set to that input. If possible, test the 1660 Super in another working computer or test a known-good graphics card in this build. A detected HDMI connection without an image can still mean the card is not completing initialization.
Try reducing the setup to the bare minimum: motherboard, CPU, cooler, one RAM stick, graphics card, and power supply. Disconnect the SSD, front USB devices, and anything else. Make sure the single RAM stick is fully clicked into the recommended A2 slot, and reseat the graphics card and both ends of its power cable. Since the 10400F has no integrated graphics, the monitor must be connected to the GTX 1660 Super—not the motherboard video outputs.
Clearing CMOS and updating the BIOS are separate things. The B560 board should generally support a 10th-generation i5, but check the board’s exact CPU support list and BIOS version if you can. Also verify the 24-pin motherboard cable and the CPU 8-pin power cable are firmly connected; the CPU power connector is easy to overlook. If it still fails outside the case, the board may be shorting against a misplaced standoff or one of the replacement parts may not actually be functional.
I had only cleared the CMOS before, so I’ll check the BIOS support information and test the system outside the case with only the essential parts connected.

The DRAM light briefly appearing during startup can be normal if it moves on to the next diagnostic stage. The important part is that the system is stopping at VGA or failing to initialize the graphics card.