Strange, I had this problem just yesterday... There are 2 different types of blue screens though, at least as far as I know of personally when it comes to Win XP. The first type is the one that says "UNMOUNTABLE_BOOT_SECTOR", which is fixed quite easily in less than 15 minutes. The second displays for only an instant, then your PC restarts.
I had the latter problem yesterday. Turns out my "Windows Registry Hive" was corrupted. Time taken to fix using Winternals ERD Commander = less than 10 seconds.
If there's one thing I know about the "pros" at Computer Shops it's this: DO NOT TRUST THEM!!! You can trust a lawyer or a doctor before you trust one of these guys. They WILL detect it if you know very little technically, they WILL smoke you for all you're worth and quite often, they WILL worsen the problem or just create another problem elsewhere in order to keep you coming back for more...
Seriously, you have a better chance at emerging unscathed from the Ocavango Delta in Lion-mating-season dressed in T-Bone steaks than hearing the truth from a Computer Tech.
Indeed, consider yourself warned.
Wife/ Girlfriend/ Mistress: "That's it! I've had it! You have to choose, it's either me or that carsite you visit so much!!!"
UCP Member: "I'm sorry honey... I sure am gonna miss ya."