PC won't boot

Hi,

For last few weeks my PC has been freezing occasionally and forcing me to reboot.

Now I'm unable to reboot and the screen is blank. There is no POST beep, but there is power to the front light, HD, CD, and DVD.

I've:
- replaced power supply and graphics card with originals that came with machine. (I upgraded card and power supply a few years back).
- tested monitor and cable on a netbook and it works fine.
- tried all variations of using a single 500MB RAM in the two SIM slots (RAM 1 in slot 1; 2 in 1; 1 in 2; 2 in 2).
- tested HD with IDE to USB cable and netbook - drive is readable.

I'm guessing the problem is either:
1) both RAMs have failed (I guess this is unlikley)
2) motherboard.

Any advice?

that the CPU temperature?

Just check carefully your motherboard,processor and RAM.