My Macbook's Combo Slot Loading Drive has not been working. When I insert a disc into My Macbook's drive it spins up for about 6 seconds then ejects the disc. It's done this with any disc. even my Leopard installer DVD. Has anyone had this problem before? I'm thinking of buying a new Combo drive and installing it but I dont want to dish out $100 on a combo drive when that isnt the problem.