iPhone 4 doesn't wake up from the Sleep Mode

iPhone 4 32Gb doesn't wake up from the sleep mode. When the iPhone goes into the sleep mode, I can't wake it up with the 'Power' button, neither with the 'Home' button. The phone is working, I even can hear the sound of 'unblock' slider if u touch and slide the screen at the place where the 'unblock' slider suppose to be, but the screen remains black. I have to push the 'Home' or 'Power' buttons MAAAANY TIMES to make the screen appear finally. Sometimes I need to push it 30 or 40 times!!! Or I just have to reboot the phone to make it work. But right after it goes into the sleep mode, I can't wake it again 😟 But when the phone is connected to iTunes, the sleep mode is working good (one push on the button and the phone is awaken). I tried to upgrade to 5.01 but nothing have changed. Also I've tried to synchronize the phone as 'New', but no luck again, the problem is still on the case. What I have to do? Do someone have the same problem? In Russia we have no official Apple Stores and my iPhone 4 is from Malaysia. So I can't just go to the Apple office and replace the phone. What can I do?