8gb 3G when it cuts off doesnt cut back on for awhile. iPhone 3G

Hello everyone,
So here we go. I have a 8gb 3G iphone running on iOS 4.1, when my phone gets cut off for whatever reason it stays shut off. I cant turn it back on no matter what I try. I try holding down the power button and home button to hopefully reset it but I have no luck.
My phone is not jailbroken and I have attempted to restore the firmware but that didnt help any. I have also attempted to let it charge overnight for at least ten hours and I have also tried seeing if itunes will recognize it. No luck with anything.
My phone can take up to two days to cut back on! Once its off I just leave it alone and pray it comes back on. When its on the charger I see no indication that its charging and theres just this black screen of death. No apple icon or anything.
Heres another problem, when its on and goes into autolock the phone cuts off. I have disable the autolock so it wouldnt cut off that way. I think im able to put it to sleep at some times but most of the times that just cuts it off.
If theres not much to do, would it be safe enough to just leave it on and not cut it off? If sleep mode works I could just keep it on that when I have to turn it off?
iOS 4