Since i had it in june, n idk what happend with yours maybe you installed some apps/hacks designed for the 3gs on accident? that would put it into safe mode and sometimes mess up the bios but it should all be fixable with a simple restore via itunes. I honestly dont think it died due to jailbreaking though, I use my iPhone 4 to teather to my laptop at my girls house cuz she dosnt have internet and i couldnt do it with out a jailbreak, well i could but apple would limit me to 2gb per month because i am grandfathered into the unlimited data plan.