Do you know M/B manufacturer name?
Some M/B use to present this strange behavior.

Do a small test: Remove all memory sticks AND turn PC on.

Your M/B must be at least beep to alert you the memory missing (im thinking that your mobo has that feature - some crap ones dont have)

If MB beeps, at least its alive.

Because if you cant get vga signal, no beeps, everything turns on and HD light remains constant on (or off) looks like that your MB is dead.

as Dr Bones "He is dead, Jim"