Sounds like either the cord your using is for charging only or your computer does not have the necessary drivers to talk to the phone. Try using a different cord first. Then use a different USB outlet. If still no then we got to get a little more technical.

You not the only one. My friend has the exact problem. Really hard to say if its the battery or the OS. The OS controls the battery, so the one way to know is to downgrade the OS to an older version. But even then there were battery problems. Hmmm, might be the hardware of the phone.

If this started to happen after the new battery then perhaps take out the battery. It may not seems like the battery could be doing this because its just a battery. However, the battery is also a computer. There could be mis-communication between the two hardware. Or your graphics driver (Kext) is incorrectly selected, Or your gpu is bad.

Go to settings, press "more.." select USB Connection, press button, then plug in phone to pc. Also go http://www.samsung.com/us/kies/ for Kies that bypasses all that. If that doesn't work then replace your cable with a "data cable". You also might be using a charging cable which doesn't have data support connecters in it. This one will work: http://www.ebay.com/itm/MICRO-USB-data-line-general-cable-for-HTC-Mobile-phones-adapters-TOUCH-HD2-T8585-/171018490106?pt=PDA_Accessories&hash=it... I know it says for HTC, but its for all micro usb ports.

Your imei is in the inside of the phone, just take the battery out and there it is above the bar code. Sounds like you didn't put the back on correctly. The antenna is in the black piece the you remove first after all the screws are out. There are several touch connections made when re-assembling. On the lower portion of it is where the antenna is at.