[help] problem with my s4 and random reboot for sim problem topic

hi guys

sorry for my bad english first :P

so...my girl have a ****ing samsung s4 i9505 with a random reboot. the smartphone give random sim unfinded error and reboot.... i have tryed imperium v14 and v15 and last lollipop google edition yesterday, but i have always the same problem...is it an hardware problem? modem problem? i'm ready with an hammer for resolving the problem forever :p

thanks for your support