You can tell how long someone has been around computers by mentioning “FDISK” and seeing if you’re met with a blank stare. Not many people remember FDISK. But for those that do, that knowledge can still come in handy today.

Two weeks ago, I was packing my bags to head for the airport when my son told me his laptop was no longer working. Indeed, it wouldn’t boot; following the BIOS check (what some of you may remember as the POST, or Power-On Self-Test), it briefly displayed a Dell MediaDirect screen and then blue-screened. I rebooted, pressed F2, and ran the onboard diagnostics, and the hardware checked out fine. Suspecting that the master boot record (MBR) had been altered to point to the wrong partition, I attempted, unsucessfully, to boot from an old PartitionMagic CD. Because I was running out of time and didn’t want my son to be without his laptop for a week, I dropped by the local Best Buy and left the laptop with the Geek Squad.

The Geek Squad called while I was away and informed me that the laptop had 187 pieces of malware on it and that the hard disk had been corrupted. They ended up charging me–in advance–more than $300 for a system diagnostics run, a hard disk backup, and an OS restore from the original Vista CD.

I picked up the laptop from Best Buy this morning and plugged it in to see what files had been lost. At least I tried to plug it in–turns out the Geek Squad had given me the wrong AC adapter. So I borrowed the AC adapter from my daughter’s laptop, only to discover that my son’s laptop wouldn’t boot. Every attempt was met by the same BSOD as before.

After another trip to Best Buy because the Geek Squad wouldn’t answer their phone, I got most of my money refunded and Geek Squad is buying me a new AC adapter. (The original was nowhere to be found; evidently they had sent it home with someone else.)

So I decided to fix the laptop myself. I was able to boot from a Vista CD but Vista’s automatic repair didn’t work. For a couple of hours, I tried a lot of different things, including a bootable Linux utility that checks your MBR, scans all your files for viruses, etc. The only issue it reported was an inability to read the boot record, which for a while had me thinking that the hard disk’s critical first sector might simply have gone bad.

Long story short, a Web search turned up information about a Vista utility named DISKPART that you can get to from the command line when you boot from a Vista CD. DISKPART is the modern-day version of DOS’s FDISK, and I didn’t even know it existed. It allowed me to examine the partition table and even though it didn’t make it clear which partition was the active (boot) partition, on a hunch I used DISKPART’s ACTIVE command to make the Vista partition the active partition and the PC booted up just fine! Years ago, I wrote an article in PC Magazine about master boot records and partition tables and all that. I don’t remember half of what I wrote, but I remembered just enough to get DISKPART to do what I needed it to do.

Of course, that begs the question of how the MBR got altered in the first place. I suspect (although I haven’t proven yet) that it was a nasty boot-sector or rootkit virus. I’ve never run anti-virus tools on my PCs, in part because I know how to avoid viruses and have taught my wife and kids how to do the same. But just before his laptop became unbootable, my son brought home a memory stick containing a file that his teacher had copied for him off her PC. Sure enough, I scanned the memory stick and it was infected.

I have since downloaded AVG Free–an awesome free anti-virus tool–and installed it on my family’s computers. Given that kids are from time to time going to be given files by their teachers and required to open them, and knowing that computers in public schools are like Petri dishes for malware, it makes sense to apply a little preventative medicine. I also discovered a cool Web site named Virus Total that lets you upload files and have them scanned for viruses using dozens of different anti-virus tools.

In the end, all is well: my son’s laptop is working again and all it cost me was a day’s work. But should I ever be so lucky as to get my hands around the neck of one of the cowards who write viruses that cost real people real time and real money, I’ll make waterboarding seem harmless in comparison.