My computer was not booting any more (black screen, no beeps). I tried to remove the RAM and boot and again, black screen, no beeps. Does that mean that my motherboard is dead?
I have an old ASUS A8V delux.
It could be a number of things. It is usually Memory out of place (which you said you already checked for) or PSU Voltage Drop (Under performing).
One thing that is also likely and unfortunately nothing you can do about, check for dead / blown capacitors.
The top should be almost flat (with slight indents out embossed sections depending on specification... look at the middle one) but you do not want to see any big bumps such as the first one or any leakage as the last one.
If your pc is of the P4 generation, there were MANY MANY boards that had this problem which lead to a lot of random failures as you are experiencing now. I had this problem frequently after just 6 months of heavy usage.