Well, as you have probably been told, the signed offer is legally binding on all parties. I would suggest that you start by calling the agents manager ASAP to gather more info but would not lose more than 48 hours doing that. The agent's Broker of record cannot ignore you if he or his agent received your deposit check. The Broker in legally responsible for accountability of funds and he cannot meet that if he does not respond to you. Your deposit cannot simply be returned to you without both parties signing a release without the Broker putting himself in jeopardy. Lastly, you should always seek the advice of an attorney who practices real estate law as his/her main area of law. You might want to ask about specific performance, and Lis Pendings.
Again, bottom line, talk to a true real estate attorney.
P.S. As a Broker, it is my professional opinion that there is no good reason, short of a very serious illness or accident, that the agent you have been working with has not kept in touch knowing that the P&S execution date has arrived. At the very least, another agent/manager should be covering.