I'd try and figure out what auction caused it, then carefully review their rules.. Assuming you broke no rules with your auction (from my recollection you only ever sold components and never completed non-fda cert lasers, correct me if I'm wrong), I'd then call up their customer service number, wait on hold for half an hour, then calmly and rationally explain what happened and why you didn't deserve to have you account canceled (since you broke no ebay rules)... When the customer service rep isn't able to help you, I'd politely thank them and ask to speak to their manager. Explain to the manager calmly and reasonably why you think your account got canceled, and why you feel it shouldn't have been. Explain the rules, explain why you weren't breaking them. When the manager can't help you, ask to speak to their manager. They probably won't have one handy though they'll ask for your phone number and tell you a manager will call you within 24 business hours. If the senior manager calls you back explain what happened and your account will be reinstated. If the manager doesn't call you back, phone customer service and immediately (and politely) ask if you can talk to their manager.. Explain that you've been given bad service and that your complaint was not resolved in a reasonable amount of time.. Explain that you've done nothing wrong and that no one was willing to help you. At that point the junior level manager should be able to reinstate your account.
Good luck. I worked customer service over the phone for two years and I know how difficult it can be to get help, though it's absolutely not impossible, you *can* get results from these people, you just have to jump through some hoops.