Anna University: I've discontinued at the end of my 2nd year, and now sitting in home my question is can I join another college starting from 1st year?

If you have discontinued at the end of your 2nd year, then the best option is to fill in a gap certificate and restart from the same college itself. But if you are determined to change your college then you will have to deposit the fees of the remaining year and get a leaving certificate. Using this certificate you can start applying for other colleges anytime.