Did you sign a non-compete? (If so, are you based in California?)

If those still at the company really don't like you and think that you screwed them, there are some shady things they can do to dilute you down to next to nothing. (They can sell the company you in-part own to a new company that you don't for a trivial amount. It happened to Eduardo Saverin and I've heard even Y Combinator in the early days. It sounds like the lawyer maybe wasn't good enough to prohibit this sort of thing.)

If I were you, I'd try and come to some agreement with them -- give back the laptop and split the difference in the shares. I'd also make sure not to re-use any code at the new company, as that would be unethical and would open you up to legal issues.