I unlocked my iphone a week ago. Everything was running fine. Today, i noticed that when i put the phone to sleep by pressing the sleep/wake button, I cannot wake it up if it wait longer than 15secs.

-Press sleep/wake button
-wait 15 secs
-press home button (nothing happens)
-press sleep/wake button (screen messes up for a sec than it reboot with apple logo)

However, if i have the cable plugged, the phone sleeps fine.

I tried restoring, but still getting the same problem.

Anyone have any idea how to fix it?