Hi Liz,
The word "intermittent" as you described your problem is, I believe, the key to finding the solution.
You and I both know that once software is configured to perform a certain way, it will indeed work that way until something changes it -or prevents it from working. The "intermittent" part of your question suggests that some software settings are changed - but then changed back - and it's all done without your knowledge or interaction. That's a rather unlikely scenario.
This leads me into one of two directions:
1. If it is software related, you may have a virus. (changes it)
2. It's possible that it's not software related at all. It could be a hardware connectivity issue. (prevents it)
I didn't answer your question to directly provide an immediate solution, but I'd like to explore these as possibilities. Based on my two areas of focus, is there anything else you can add that may help narrow it down (or eliminate these)?
Leave a comment (or email me) and I'll leave additional comments as appropriate.
Maxwell