iPhone turns off

[Shavon]

I got a iPhone 3G 8 gb and for some strange reason, the phone always goes black screen whenever a boot or reboot happens. I bought it off of craigslist and was stuch in recovery mode but after getting through error 1015 and numerous other erros, I finally got it go through. But now it just dies whenever the screen is not in use and I've tried putting auto-lock to never but that did not work either. I took it to a phone store a friend works at (not Apple since its unlocked for T Mobile) and even they were not able to fix the issue. The screen usually has this strange white screen everytime it restores or I kick it out of recovery using Tiny Umbrella. I got it to downgrade from 4.2 to 4.1 through pwned DFU Mode in redsnow but still problem exists.

Any help would be appreciated.
Thanks

Anyone got a solution or suggestion?