I've been building a C2Q Q6600 system, it won't boot. Its an MSI MS-7380 motherboard

I got the correct ram (works in another PC), changed the CMOS battery, cleared the CMOS, tried a PCI graphics card in both slots, tried with and without HDD. Also tried PCIe gfx card. Tried a def working CPU from the other system. PSU runs the other system fine, its 450W.

A LED on the board comes on, and a blue one also when powered on. CPU fan runs, CDROM light flashes, monitor light comes on green for about 3 secs then goes orange. Nothing at all displayed on monitor.
No beeps from speaker.

The PSU I am currently trying to boot it with is 450W 24pin, it was previously running my other Q6600 and drawing approx 170W running on full load. The first cpu I tried is now running fine in the other system. I tested the RAM in that system too. The MSI board (that doesn't boot) has an 8pin connector for extra CPU power, which I have connected via an adapter to the 4pin connector on the PSU.

My working q6600 PC is currently running on a 250W PSU, I changed it from the 450W to try on the MSI board as it has 3 PCIe x16 slots, the reason I bought it, to fit more graphics cards in. I'm only trying 1 gfx card when I'm trying to boot it ATM.

In short, the CPU, RAM, GFX card, PSU all work on another machine, but on this mobo, no luck.
Anything else I can try before I tell the ebay seller its dead?