I'm in need of help... I'm at the end of my tether.

My computer recently started behaving oddly. Sometimes it simply would not boot and by boot I mean it wouldn't show anything on the monitor, no bios screen or antying. All the fans and hard disks were spinning, the Power on the mother board showed green, but nothing else. Then seemingly at random it would start working again, sometimes I would have to turn it on and off 50-60 times or wait a day or so, but once running again it would happily run for days on end, as long as I didn't turn it off completely (reboot was fine).

I tried switching out my graphics card, but that didn't help, so I assumed it was the motherboard. Being a machine of some 4 years I went he whole hog, upgraded the the CPU and the motherboard.

Now I am getting seemingly the same problem, the system will boot randomly and runs fine when it does, but sometimes I just cannot get it to boot at all. On my new board I have a the CPU_LED lights up red, I get no sound out of the speaker I attached; I get one short beep when it boots normally.

I left my bios config as standard (from when I can get it to boot), and have tried resetting it

I've done the usual of unplugging everything not core to the system, trying both none and one memory sim, using onboard graphics as opposed to card etc.

I checked the cables connecting to the monitor by running from an old laptop and no problems there, works fine every time.

Specs
memory: 2x4GB Corsair Vengence
motherboard: Asus P8Z77-V
cpu: Inter i5-3450
graphics: ZOTAC - NVIDIA GeForce GTX 460

Any thoughts on what it may be greatly appreciated...

Have you check the memory?

I have had memory to go bad, and the PC just not boot because of it.

I am assuming you dont get the POST sound?

I would take one out at a time, switch them to see if one module is bad.

No POST sound.. the memory is brand new - I replaced it when I replaced the motherboard. I've also tried with no memory and with just one module and switching them, but still no joy.

Might sound stupid

Have you checked to ensure you have connected the 24 pin to the mothoboard and the 8 pin?

Some times people will forget to connect the other and it will not boot.

Also, you are running some decent specs. What's the rating on your power supply?

550 watts should suffice with one card.

If you have two, I would say spring for a 750 or higher.