Right, I'll give it a go at the weekend. I was looking it up on a few of the PC forums and kept seeing horror stories from people where their PSU sparked and smoked. I had a nightmare trying to install the CPU fan (hyper 212 evo). I put a bit too much thermal paste on (or so I thought), I was told to let the pressure from the fan installation spread the paste so just did a slightly oversized pea in the middle. I then totally cocked up putting the fan on, I didn't realise a notch wasn't sitting in the hole for the 1150 board and I was told it would require pressure so didn't think too much of it. Anyway, after a week of worrying I took the fan off, cleared up the thermal paste which got on the cpu clamp after I twitched I think I have it fitted properly this time with less thermal gunk all over the place. But that is mostly what scared me from turning it on for so long.
Also had a bad time trying to line up the damn motherboard properly too. Felt like I was messing everything up. I was sweating like mad. Kind of regret not just buying one from PCSpecialist or something now, at least if it messes up I could send it back.
Assuming the PC works fine, I'll go ahead and buy windows to install onto it. Just wanted to make sure it booted first before I spent £80 on the OS.