I was having issues with my Samsung s3 as well. I wanted to be able to connect my Samsung S3 to my PC so I could share my computer's Internet connection with my phone, it took a little while to master it, I didn't know that you could connect the phone to a PC via USB, after some searching online I soon discovered I could by going into settings--Developer Options and turned it on, then I went to settings--more settings--tethering and portable hotspot and turned on USB debugging.
Finally I thought I would be able to share my PC's connection with my mobile, I was able to connect to Facebook and search the Internet, but for some reason I still couldn't sync my email account which was strange. I was being recognized by my PC since it was there under "Portable Devices" I was able to access all my files, I have Kies installed, I knew I had all the latest drivers. I have always used mobile data or WI-FI to connect my phone, which is convenient when your out and about, but when you are home and have access to a PC it makes sense that your phone be able to connect to it.
So I came here in search of answers, and after reading through all the comments and realizing there was something I was something I was missing, I took the advice from peteyw85 searched my "device and printers" section in Control Panel and realized that not only did my Samsung S3 device appear but also two previous mobile phone devices that I had connected to my PC. Once I removed the two other devices I now longer use now, my phone finally worked and connected to the Internet and my email account was able to sync once more.
I don't know why my PC couldn't tell the difference between my new mobile and my previous devices, but I am hopeful that maybe this can help someone else.