How can I get my money back?

My landlord needed a big amount of cash so he borrowed from me and deposited a check to my account with the same amount. But his check was rejected by my bank because there was not enough balance in his checking account. I've been asking him to pay me cash back for days, but he kept saying he would yet never actually did. Yesterday he came back with another excuse that his ex-wife for some reason froze all his bank accounts.
There's been some very negative impact on my own finance, not to mention the time and worries involved, so I'm seeking legal help to resolve this as soon as possible.

I'm wondering what should be the first couple of things I need to do. Should I write down what happened in paper, and have him sign in front of a public notary? Or should I just go get a lawyer? I'm not even sure which legal area I should look into, civil rights? Please help me...