hmm. have u rooted ur phone? or did u buy it used or something? that warning triangle symbol usually comes after u've rooted ur phone.. there's a way of removing it, but u shouldnt have it if its brand new, and u didnt root it urself

 

Yup, heshanj is correct.

This symbol means that an insecure (ie rooted) kernel has been installed. If you didn't do it yourself, something fishy is going on.

If you did, then it's easy enough to remove. Go to the All Things Root sub-forum here and follow the rooting guide. It's simple enough to do.

 

rooting is a process that gives u access to pretty much everything in ur phone (root access). its a process that generally voids ur warranty... and u should never get a brand new phone thats rooted. most of us users root the phone anyway, but this means that ur phone has been used before u bought it.

i havent used Kies since the first day i got my phone so i dont know why its not connecting, but i assume that since the yellow warning triangle is showing on boot, ur using an insecure kernel and ur phone isnt being detected by Kies.

do u see an app called Superuser on ur phone, in the app drawer? an app called CWM?

depending on which method ur phone was rooted, u can remove the warning. but i cant remember how to check if ur rooted with CF root or superoneclick.. anyone? i think if u have CWM app in ur app drawer, then u've rooted with CF root. let me know so i can post the relevant instructions to remove it

 

hmm well ucould ask him. rooting does void warranty generally, and even if u unroot it, its probably not good enough. anyway, dont worry about it, ur phone will be fine

if u see the superuser app and not CWM, u were probably rooted using superoneclick. if possible, u could ask ur bro if he rooted it, and using which method, to be sure. u can remove the yellow warning by going to this link
[ROM + Guide]Official i9100 Firmwares KF1/2/3/4/, KG1/2/3/5/6/7, KH1/2/3/4 Download - xda-developers
u need to just flash the stock kernel for ur firmware, using Odin, in the last step of the Quick Root guide in that link.. hope this helps

 

the yellow triangle shouldnt affect ur phone's perfornace, i dont think u'll have any problems with it. but u might want to know wat firmare ur running: type *#1234# in the phone's dialer and see wat u get

im not sure if ur phone is unlocked or not, unlocking and rooting are two different things. ur phone is definitely rooted, and although that might void ur warranty, u'll notice there's a lot more u can actually do with a rooted phone