How can I restart TSP after having a TSP hardship withdrawal?

If it was a withdrawal, not hard at all. Simply start contributing again.

SSG (Join to see), I looked into it before. After the mandatory 6 month period (where you can't contribute at all) after you withdraw money you can re submit your contribution form. If you take a loan you don't have to worry about the taxes and stuff. I think it is still cheaper to do the loan vs. the withdrawal. Hopefully somebody else can verify that.