Landlord backs out of lease day after lease is effective

I am a graduate student in Washington DC. I signed a lease for a room in a house in DC back in June, sent in my security deposit and a check with first and last months rent (as per request of landlord). The lease was meant to start on August 1st.
Five days before the lease became effective, the landlord sent me an email telling me that my checks were non-negotiable, and if I did not send him a cashier's check by Aug 30 the lease would become invalid. Due to travel, I did not receive this email until July 31, at which point I tried to call and email him multiple times, and he did not respond.
On August 2, he finally responded to my phone call (when I used a number other than my cell number), and informed me that he no longer had room for me, and that I needed to find another place to live. When I asked him about the email in which he stated that I would have until Aug 30 for the lease to be terminated, he told me it was obvious that he meant July 30.

Are there any actions I can take against him or any ways I can warn other students of his shady actions?

It was obvious that he meant July, not August. Why would anyone rent to you with no money for the whole first month? No one pays rent for the month AFTER they've already lived there. Rent is ALWAYS paid in ADVANCE.

What do you mean by a non-negotiable check? Do you mean there wasn't enough money in the account (a bad check)? You gave him a worthless check which he couldn't cash. He contacted you and informed you of such. It would be reasonable to believe that you had to make good on that check before you could move in on August 1st. Most LLs only give you 24-48 hours to make good on a bad check. On the beginning date of the lease, he had no money credited towards the unit. Therefore your lease was cancelled since you did not meet the requirements to take possession (deposit + 1st month's rent).

What action do you think you can take when you didn't pay for the unit? How is he shady when he held it for you up to the date of occupancy? He probably thinks you're shady for trying to give him a bad check. Why didn't you know that your check was no good? You had all of June and July to realize it and fix the mistake. Didn't you balance the checkbook once in that time?

My check was good. He never tried to cash it. He had it in his possession from the middle of June, and never made any attempt to cash it. There was no reason for him to assume that he would be unable to deposit my check. I informed him as such in an email.

Once again, in case that wasn't clear, I wrote him a valid check, and he decided it was "non-negotiable" without any basis.

I paid in advance. He deposited my security deposit. He had my money. He canceled my lease without informing me that he would do so, and avoided any contact with me when I tried to speak with him.

He had to have some basis to claim the check was non-negotiable. I can't believe he made that up for no reason. (I doubt a judge would either.) Why did he tell you he couldn't cash the check? He had to give you some reason. He even sent you an e-mail asking you to make good on the check within 5 days. If he was going to just cancel for no reason, he wouldn't have done this. It shows good faith on the LL's part to offer to allow you to make good on it.

It doesn't matter when he tried to cash it. It is his perogative to cash it immediately or hold it until just before it was move-in time. (Many LLs would hold it for a period, to see that the last tenant vacates on time, then cash it just before move-in to be sure it is good.) There must be sufficient funds in the account to cash it at ANYTIME it is surrendered to the bank. Once a check is written, it is as good as gone from the account (no matter what your balance may say).

So why couldn't he cash it? Was it written to the wrong name, unsigned, a wrong date, what? And please explain how he cashed your deposit but not your rent? Did you give him 2 checks? One didn't clear but the other did? Why didn't the rent check clear? If you wrote 2 identical checks, one cleared, the other didn't, there can only be one explanation. there wasn't enough money in the account for both to clear.

You said he didn't tell your lease would be cancelled if you didn't make good on the check. Do you think the car dealer would let you have your new car if they couldn't cash your check? What if they told you to fix the problem before delivery of the vehicle and you didn't. Do you think they'd still deliver your new car?

He never tried to cash the check. He asked me two weeks before if it would be ok to cash the check, and I told him there was more than enough money to cover it.
As soon as I read his email telling me the checks were non-negotiable, I called him, and he never called me back.
I understand that you think that whatever this landlord did was with good reason, but I can honestly tell you that I did everything I could to show him that I would be following through on the lease, that I had enough money to pay for the room, and that I am an honest person who would do nothing to hurt him financially.
I was supposed to live with another student in the apartment, and he knew that we had made this agreement together, yet failed to tell either of us that he had changed his mind.
I just want a way to warn others of his shoddy practices so others aren't lulled into the false security after entering into a lease agreement with him.

You come across as honest and sincere (and you didn't get defensive when I suggested that the check wasn't good). That tells me loads about your character. I believe you when you said the check was good. You are entitled to sue the LL for failure to honor the terms of the contract. Once a legal contract is signed, neither party can back out of it without just cause. If you truely had enough money in the account, he would have had no just cause to demand an alternate check and terminate any signed agreement. Get a statement from your bank to show that there was enough money in that account, and sue away!

In order to warn other students, you might want to approach the student services of the university you are attending, specifically the housing department. Many large colleges have a person in charge of approving nearby rentals for students and keping a list of those rentals in case a student needs to find a place quickly. They can either remove this LL from that list, or serve as a warning to others that he broke his contract with no notice, leaving a fellow student without housing (even though it had been reserved and paid for 2 months prior). Ask about this at the college.