Here's the scenario: one minute you're working and surfing quite happily, the next the Blue Screen Of Death rears its ugly head and your machine won't boot.
Whatever's happened to Windows is serious and the problem is confounded by the absence of backups.
You've been promising to make some but never quite got around to it. Don't panic! Just follow these steps.
1. The easy win
Before you bring out the big guns – which we'll discuss later – it pays to explore the easy options. Try using Windows' own repair and recovery tools, accessible from your installation disc.
Depending on the version of Windows that you're running, the choices will differ. For Windows 7, the key is Startup Repair. This will hopefully "automatically fix problems that are preventing Windows from starting".
2. Leave your hard drive alone
If you're dealing with sensitive data on a crashed PC, it pays to be careful. It's safest to leave the operating system alone and try to access data, files and folders indirectly.
This is particularly true if you suspect you're battling a virus attack. By running the host OS, you give the contagion the opportunity to call home, update and send out more of your data. With all this in mind, we say don't boot a damaged OS – use a Live CD rescue kit instead.
3. AVG Rescue CD
If your PC has been brought to its knees by a virus, getting back into Windows with enough control over the system to remove the contagion can be tricky. Thankfully, there's an easy answer – the AVG Rescue CD. Download the ISO image from here and burn the image to a CD or create a bootable USB key.
Whatever you choose, the Linux-based rescue CD makes it easy to scan and remove viruses. The Inside Security Rescue Toolkit isn't strictly a rescue system – it's more a tool for forensic security analysis.
It can, for example, examine a huge variety of different filesystems, from common NTFS to more obscure systems. The toolkit will scan for viruses and let you get online from a defunct PC. It can also sniff out rootkits.
4. The Ultimate Boot CD
If nothing we've discussed so far has worked, go for the big guns. It's time for The Ultimate Boot CD, a collection of 100 applications that should help even the most knackered PC get back on its feet.
The interface breaks apps down into categories, such as BIOS, CPU, Memory and so on. Follow the menu structure. Given the number of apps on offer, you should be able to find one that will salve your PC's ills.
GParted is a classic among opensource applications. It's essentially a program that lets you move, resize, check, copy, create and delete hard disk partitions.
It's not uncommon for these to be damaged during a serious crash, so having GParted to hand as a Live CD is essential. Despite the program's obvious power, it's extremely simple to use. You can download it from here.
6. Free ISO burner
To turn an ISO disc image into a functional Live CD, you need an ISO burner. Newer versions of Windows feature such tools as standard, but if you're after something more feature-rich, try Free ISO Burner from www.freeisoburner.com. It can burn to a wide range of media.
7. Undelete a file
Pandora Recovery can resurrect deleted files. Use the portable version – installing it natively risks overwriting the data you're trying to rescue. Get it from www.pandorarecovery.com and build a bootable USB version of the program on another PC.
8. Ghost for Linux
Norton Ghost is a classic application – we've used it and loved it since version one. It's a partition-cloning tool and can be vital in a disaster. To experiment with the concept of partition cloning, try Ghost for Linux. It's an open-source project and you can download it from here.
9. A beeping PC
If your PC does little more than beep after its crash, it's sending you an encoded diagnosis of its ailments.
All you need to do – albeit from a different machine – is visit www.computerhope.com/beep.htm, where you'll find a complete guide to beep codes.
10. What went wrong?
When you're back up and running, you need to work out what caused your PC to fall over. Here, the Windows Crash Dump is your friend. Microsoft does offer some help, but for the ultimate insight, visit Crash Dump Analysis.