It sounded to me you might need to hard reset your phone. Refer the link below;

http://www.hard-reset.com/samsung-i9100-ga...hard-reset.html

Warning: You might loose your apps

Anyone got any better idea?

I did try on my father's laptop, which has XP instead of Vista (my laptop). I installed Kies on his laptop, and plugged in the USB, with the same result as with my laptop (can't detect the right drivers to install). Again, I deeply suspect the firmware is the culprit here, cuz there is a user who posted here previously that have no such problem until the upgrade to DZKJ2.

Yes.go ahead and try kernels.the best battery saver kernel I have used over stock Rom is superkernel v 1.1 .on outset its governor is "powersave "

For battery life u can also get into setcpu and juicedefender .see post 817 page 41 .

If there is time I d try put together a guide.I agree battery life of 8 hours is no go.I don't like extended battery or spare battery or carry around charger too

I got it from the facebook group. I already used it. Somepone modified it for GT-I9100G.