Dead RAID.
RAID? Redundant Array of Inexpensive Disks. In reality it's not entirely Redundant, especially if you are a boy racer such as I and use RAID-0. And it's certainly expensive to such morsals like myself.
I was playing Freelancer (yes, I'm strangely addicted, as it's dead boring) and my hard disks made funny noises and my computer died, so I thought I'd improve cooling on my computer. A week later I tried again and all was fine, but then it died again. Second time round my computer wouldn't boot saying a stripe (RAID-0 means 2 disks are used, and striped) had been removed.
Oh how I felt bad, I mean really bad. First panic, then horror, shock, and finally bereavement. But joy oh joy all hail Highpoint Technologies. They were kind enough to send me a little app they were working on that rebuilds array. And woohoo, it's back, almost perfectly. I was missing the software hive of my registry, and I stupidly over-wrote it with an emergency recover one before I realised I should have checked the disk on a low level to find it. But hey ho, my machine needed a reinstall anyway. It had been on the same build for almost a year (with no problems which is more stunning).
It allowed me to try out a slipstream Windows install (service packs and drivers applied as you install and not after in pain staking process of rebooting lots).