I am sorry to learn of this situation. You should have received notice of your delinquincies prior to this (the "Notice of Trustee's Sale" is one of the very last notices you receive, not the first).
See: http://hoalaw.tinnellylaw.com/2013/08/hoa-collection-procedures-stri.html for a discussion of each of the notices you should have received and why proper compliance by your HOA is so important (as well as what you can do if you did not receive this notice).
However, if you simply did not address the problem until now, you can still try working with the HOA to come up with a solution - an HOA is not likely to want to have to deal with a trustee's auction, so if you have a reasonable plan to pay off the debt in a short period of time (think get a loan from a friend/family member/bank, make very significant payments on a payment plan (this won't be easy to do, I understand, but you are trying to avoid losing your property)), the HOA may be willing to enter into a settlement where they cancel or postpone the trustee sale while you try to make a payment arrangement with them.
If you do reach an agreement, make sure to get it in writing.
If your finances are in very bad shape, you may want to consider filing bankruptcy, if so, file well in advance of the auction date - while it is possible to show up on the day of the auction with your bankruptcy notice and stop the sale, this is a very risky practice - if you are even a minute late, or if you show up at the wrong place and the trustee does not receive notice prior to the sale, your bankruptcy will not stop the sale.
It is possible to file for bankruptcy protection yourself (without a lawyer) - see: http://www.uscourts.gov/services-forms/bankruptcy/filing-without-attorney it is not recommended (especially if you are trying to avoid a foreclosure sale on your property), You can find local bankruptcy attorneys using the State and local Bar Association directories, or private directories such as www.AVVO.com; www.FindLaw.com; or www.Martindale.com (I personally find www.AVVO.com to be the most user friendly).