lol Because, Gary, computer tech geeks (like I used to be) don't like to admit powerlessness over a computer or tell you "I don't know." And, when you're getting paid by the job instead of the hour (which seems to be the trend now), what they're looking for is the quickest fix. So, that would be the answer to your question 95% of the time -- I don't know, but won't say that I know, and tell you what will surely fix the problem, which is to reinstall windows, so we reinstall EVERYTHING because one or two things is out of whack.
The other one I like, btw, is that it's the "motherboard" or even better "your BIOS". They like to say that because that is something they CAN'T fix! Of course, with this particular one, there is probably a 60% chance it's a cop-out instead of the whopping 95%.
So, these computer geeks tell you it's your Windows installation or the BIOS because they are too lazy to figure out what's wrong, or too proud to admit they don't know.
-- ADDITION --
Heeehee ol' Spark got the same answer posted just a few seconds before I did.