Computer will not boot to BIOS
If you remove all RAM sticks from the motherboard,
and the boot up attempt then does not indicate memory-problem with beeps,
it is very likely that you have problems with the motherboard power regulation components.
For example, take a look at the capacitors on the mother board near the power-supply cable connector -- do they all look fine? are any of them discolored, out-of-shape or 'leaking'?
If you do not get memory-missing/failed beeps when you boot with no memory,
it is very likely that the POST (power on self test) of the motherboard never started.
If there are not problems on the board, you need to look at the power supply itself. Maybe the lower voltage power rails for the processor etc have malfunctioned. This would let the fans work but will not power the CPU (for example).
It's time to start swapping components. I'd start with the power supply first. No need to take the old on all the way out of the case, just take a known-working PSU and plug it into the motherboard. Start with the power supply, then try the video card, then the motherboard.
Once you find the faulty component, replace it and through your known-working spare back in a safe place.