There are certainly some reasons why WMM is crashing on you. Unfortunately, WMM (and Windows) doesn't give you much of a clue on what those reasons are.
Since there aren't many free (no cost) video editing programs and switching to a different program involves a learning curve, I suggest reading this thread if you haven't already done so:
WMM FAQ.
That being said, aside from getting the popular NLEs (Non-Linear Editors) through illegal sources, there are a few no-cost programs listed in the
Software Lists thread.
I'd recommend getting a copy of Magix Movie Edit Pro for $50 (or less, if you can find it on sale).
For this week (Dec 9 - 15) Best Buy has Sony
Vegas Movie Studio 8 and
Vegas Movie Studio Platinum 8 on sale for $49.99 and $59.99 respectively. If you can somehow scrounge up $100, I think the
Vegas 6 deal is still available.