Well, there are sport bike experts here that can help answer your questions. There are utility bike experts that will offer help as well when they can. You can get a service manual for your 300EX HERE
Does it have spark? Need a carb cleaning? Motor seized up/needs rebuilding? Start a new thread in one of the relevant technical forums
, list the year & model of your bike again, why it was parked (and how long) and every issue you'd like to fix... and we'll be right along...
Let us know how we can help you..? If ya post pics your thread will become irresistible to many/most... LOL