I got this PC Compaq Presario 7170, which had a problem with mouse port. It didn't work. Serial mouse is working. I...

I came across one old and rare laptop but it has a screen problem. Now, I don't own this yet, but wanted to hear for...

I have this very old laptop Compaq Armada E500 (not 7800!), which has only one USB port (I think it is 1.1 standard). As...

Ok, so the problem was this component right here: The voltage was dropping on it, so I removed it (wire jumped) and now everything is working. Including mouse. :)

Update: I have 5V when the keyboard is not connected, so that should be fine. But I red online that this could be due to faulty transistor that controls the voltage. Now I should find this transistor but I don't know how. :(

I just discovered that I have 2.5V between DCC and ground pins on the keyboard connector. Based on the schematic, it should be 5V. Could this be a issue and what can I do to track down this problem?

The RX 570 requires minimum 450 W PSU. You have 500 W one, but what is the your PSU grade? Is it a gold or platinum variant? I would suggest you to find a friend or someone who can borrow you a good PSU to try out, or you take your GPU to a friend to test it on their machine. In what you described, this seams as a power problem to me. Ofc, before you swap PSU, please update your system to latest updates + latest drivers for your devices.