Phone keeps going into DFU mode

I have a never unlocked iPhone 4, it is running 4.2.1(8C148) with baseband 3.10.1. I am currently using the gevey unlock sim. Was working great for the last 6 months. Now it is acting strange by spontaneously going into DFU mode. The screen goes completely blank, does not turn back on. I have to give it a few hrs rest, and then I can turn it back on!
When in DFU mode, if I connect to iTunes, it askes me to restore the phone with 5.0.1 software. (recevery mode)
Do u guys think it has something to do with the gevey sim card?
I have not jailbroken the phone ever.
Is there a solution to this problem?
Thanks.

Does it continue to happen if you remove the Gevey SIM? That's a quick way to test. I know the phone isn't useful without it, but in the interest of troubleshooting...

yes, i did remove the gevey, but still happenning.

Most likely a hardware issue then unfortunately. This type of issue can be related to the battery, if you've been having battery issues prior to this happening it's probably an indicator that it's time to replace the battery.

thanks for the info.
any suggestions of a battery replacement place?
i bought this on ebay

battery was holding charge fine prior to this happening.
yesterday, I found the phone to be extremely hot! and had discharged the battery completely. I charged the phone and after 1 of its cycles :( turned it back on.
now i do find the screen "flickering"--- never happened before.
looks like whatever the problem is getting worse! :woz:

Almost guarantee it's a battery issue. Buy a genuine Apple replacement battery online and replace yourself (kind of a hassle) or just bring it to an Apple store and have them replace the battery. Non OEM batteries cause issues in a lot of cases. Sure, you could be lucky, but it's a crapshoot. I recommend a genuine Apple manufactured battery.

Quote:

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Originally Posted by mas8002mi

I have a never unlocked iPhone 4, it is running 4.2.1(8C148) with baseband 3.10.1. I am currently using the gevey unlock sim. Was working great for the last 6 months. Now it is acting strange by spontaneously going into DFU mode. The screen goes completely blank, does not turn back on. I have to give it a few hrs rest, and then I can turn it back on!
When in DFU mode, if I connect to iTunes, it askes me to restore the iphone with 5.0.1 software. (recevery mode)
Do u guys think it has something to do with the gevey sim card?
I have not jailbroken the phone ever.
Is there a solution to this problem?
Thanks.

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DFU mode is a hardware failsafe, the hardware is designed to only enter this mode if something is wrong with startup.