Bad Check? sec. 1, NRS41.620

I received a check via UPS Next Day Air, I wasn't at home so it was signed for by a agent in my leasing office at my apartment complex.
When I went to get it, I opened it and inside was a check for $2500. I showed the leasing agent and he said I was the luckiest guy he knows.
I wasn't sure who the business was that the check was from and there was was nothing else inside the envelope, but the check. The check was made out to me and addressed to me. I fill out a lot of offers and sweepstakes on the internet and thought it was just my lucky day.
I tried everything I could to look up and contact the business that the check was issued from, but had no luck. I ended up calling the bank that the check was drawn on to verify funds. The customer service agent ask me the account number on the check, the name of the business and the check number. I gave it to them and they told me funds were available for the check.
I called my bank, not being from the state where the check was drawn to see how long after I deposited it would the funds be available. They told me up to 10 days, but I could take it to a check cashing place or a local casino and they may cash it immediately. I took it it to a casino and they cash it with no problem.
But, now I received a certified letter from the casino saying the check was returned and that if I didn't pay the full amount they would refer it to the District Attorney, stating that according to Sec. 1, NRS41.620 I committed a felony.
I have no way of paying this within 30 days and don't even know if I'm legally obligated to.
What should I do?
If you have any suggestions please contact me at:
lestat1@rock.com Thanks....

This just happened to me today I received a check for $3,650.00 From a unknown company stating i won a lottery.
Guess what I do not do lottery or online games nor anything like this.
I went to key bank the bank that the check was drawn on and asked them on the spot to look up this account guess what it was a fraud just like i thought it would be. Lesson to be learned if it looks to good to be true it is.