iPhone 3G Stuck in Sleep,wont wake PLEASE HELP

[Tahie]

Everytime my phone goes to sleep it freezes and it wouldnt wake-up again none of the buttons work and the only thing i can do is reset the phone by holding the Power button & the Home button, but again after it resets once it automatically goes to sleep or i press the sleep/power button and wait for around 10secs it doesnt wake-up again..i tried restoring the software many times and i upgraded to OS 3.0 but im still have the same problem,
i noticed something though,when i phone is connected to the computer this doesnt have and the phone wakes normally...
p.s: my phone is out of warranty so taking it to apple is not what i can do
PLEASE HELP