Problems: iPhone shutdown every time its sleep

I've found this problem on my pwned iPhone fw2.1 and problem still there even after upgraded to 2.2 using Pwnage Tool..

The problem is the phone will shuts itself down every time that it sleep regardless it is on auto-sleep or when I press the sleep/wake button.. so, now I have let my phone to stay awake at all time.. and its really drain my battery! :(

Any idea how to fix it?

Thanks,

first and foremost chances are this is indeed a hardware problem provided that if you have been suffering this since the older updates pre-2.0 FW or that some application is actually bugging up one of your system plists thats making it act that way if so you could try to remedy this by going back to either 1.1.4 or 1.1.5 if it exists and unlock it with ziphone should this work then it is highly likely theres an application thats killing the plist
better if you could shed better info about your iphone whether if it is 2G or 3G