OK this is freaking me out. You've probably guessed that I'm not a techie nerd, but I'm not daft either. I know how to follow instructions. So I surfed the net to find out how to check the bios set-up, and the consensus was that I should press DELETE or ESCAPE when the PC fires up (i.e. when it starts checking the memory etc). Only thing is, when I unplug the PC, leave it 1 minute, then boot it up again it goes straight into the Windows XP welcome screen - it's as if the thing isn't shutting down properly even when I detach it from the electricity supply! So how do I enter the bios set-up if I can't get the thing to shut down properly in the first place!?!?
By the way it DEFINITELY doesn't have a standard on/off switch. It's an Emachines 270 from PC World in the UK. PC World are the UK's biggest PC retailer by a mile so they're not some dodgy back-street dealer. The new PSU is a "Q-Tec PSU 450W Dual Fan PFC". I hope that helps!