My best friend all of the sudden dropped me out of her life for no apparent reason. What should I do?

We had been friends for over 10 years. We’ve had kind of an on- again, off-again friendship. (we’ve gotten mad at each other before and went a year without speaking) This time though, she deleted me off facebook (and blocked me), removed me from myspace, and won’t respond to my texts. I have no idea what I did or why she is mad. What should I do? I would like to save our friendship, but at the same time I’m kind of pissed she drops me for no apparent reason!