Contact the test administrators immediately and explain what happened. The fact that the failure of their device cost you time in both sections (not to mention the general stress) should definitely be addressed by them. I don't know how they would address it but, if this had happened to me, I would at least ask for a free re-take of the test.
I think it's doubtful that they will cancel the test score after the fact. They only do that in the rarest of circumstances. If you had declined to continue working on the test in the middle (so that a "cancelled test administration" would have appeared on your record), then you might have had a shot at getting them to remove that from your record, especially if you filed a report at the test center and explicitly stated that the reason you were stopping your test was the technical issues they were causing for you.
Contact them, explain the case, and see what they offer.
You mentioned that you were re-taking the GMATPrep exams. Were you also retaking the MGMAT exams? What did you do when you saw repeated problems? Specifically, did you always get them right, regardless of whether you'd gotten them right before? Did you take normal time to answer or less time than you would have if it had been a completely new question?
If you were answering questions correctly that you should have been getting wrong, or if you were spending less time than you would have under normal circumstances, then your practice test scores were likely inflated. Unfortunately, it's impossible to tell how much.
If you were not doing those things, though, then your official score definitely represents a big drop from your practice scores on the verbal. In that case, we need to figure out why this happened. Part of it, obviously, was the palm scan issue - the stress and the time it cost you at the beginning of the section. There are probably other factors as well, though. Read this article and do the analysis described, then come back here to report your findings:
http://www.beatthegmat.com/a/2009/10/26 ... went-wrongIt is possible that one of the causes was a timing imbalance. Because you knew that you were often too slow, perhaps you sped up and actually went too far in the other direction, answering questions too quickly and making more careless mistakes than usual. I see this happen a lot in practice. A lot of times, students will first try to speed up on the ones they think are easier, thinking that that's the easiest way to save time, and then they make more careless mistakes on the ones that they really do know how to do - and the score drops. It's possible that you did this, too, except you did it on the real test. (The better thing to do is to identify those ones on which you're spending too much time and cut those off more quickly.)
Anyway, go contact GMAC and Pearson, and then let me know on all of the above other stuff.