Drive tray is not opening,Different problem

Hello,

Sony DVD drive tray is not opening, initially i thought it must be drive problem, so took it to claim under warranty, there they checked for faults, but no faults came ,it worked perfectly.The technician said it must be bus problem, so i bought new bus, after installing new bus it was working good for a while, later again the same problem popped out. Now i again i replaced the new bus with the old bus, the problem was solved temporarily, latter again the same fault appeared, now again i replaced it with the bus that i bought previously as said, now its working. so i came to a conclusion that there is no fault in both buses. The sata ports of my motherboard are working perfectly when checked with hard disk, the Sony DVD drive that i use has sata connectivity. please do suggest me what would be the fault?? thanks in advance