Nope, that's a fairly standard setup - you can usually change it in the BIOS, but it's so that (among other reasons I'm sure) you don't shut your machine down if you accidentally knock the power button. Trust me, I've done it enough times.
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The replacement CPU I ordered via eBay finally turned up today (and as an aside, isn't it infuriating when you need something quickly and the seller sits on it for the best part of a week before dispatching it?).
Swapped it over with my existing CPU, and exactly the same response - no post beeps, nothing on the screen, PC sitting there like an oversized paper-weight.
So, unless it's some truly bizarre incompatibility issue, the motherboard must be DOA. I've sent scan a message via their website detailing what I think is wrong, and what tests I have run, and I'll just have to wait and see what they say.
Thanks to all for your ideas and support - I'll let you know when I *finally* get my PC up and running.
Just a quick update in case anyone faces similar problems:
Scan finally got round to testing my motherboard today (It's been sat on a pallet in their returns department for the best part of a week), and it is now officially faulty. Hurray!
Unfortunately, Scan sold out of that particular motherboard this morning, so I've had to take a refund and order a replacement elsewhere. Why on earth they can't reserve a replacement item when someone returns a faulty product I don't know...
Anyway, assuming the courier is reasonably speedy, I should have a functioning PC by this time tomorrow, a mere three weeks after I ordered the blamed thing.
Thanks again for all your help.