There is a prompt that shows up on the dvd screen to press ok as soon as a disc is inserted, however i am not able to press ok with the remote. The player itself and headsets work fine. Could it be the remote battery? What size is the battery?

 

I had the same problem with mine a few weeks ago. Took it to the dealer and they replaced the battery, works like new again! I don't remember what the battery size was.

 

Sounds like you need a new battery

If you're unsure on how to open up the battery part of the remote (pretty easy BTW), take it to a Radio Shack and they'll do it. They have the battery in stock and will even install it for you (also very easy) ~$5 total.