Good answer to "why" questions (especially this vague)?
"I don't have a clue."
It's really a good answer, and 99% of the time, it's the truth. I had it explained to me this way by an instructor, and it clicked. It took 5 years and 10,000 different people to create windows 2K. That's the OS alone, not 3rd party vendor drivers or any add-on software. Much less the hardware itself. These numbers may not be accurate, but paint a good picture.
How the hell is any one person going to be able to explain how all these things interact? You aren't. Knowing how to find information to fix something is much more useful than knowing "why" something happened.
It could be one of a million things. Bad: user software, memory, HDD, data cable to the HDD, virus, spyware, software diver, etc, etc, etc.
Are you willing to track ALL these things down (some of which you don't have access to key information like source code), or just fix the problem?