hi chandru,

300 marks in boards is 60% if total marks is 500 which made you not eligible to get into IITs/NITs/IIITs. 39.6 percentile is more than 6 lakhs rank which will not fetch you good colleges. With pwd quota  you can get a few good college like NSUT which has only 60% eligibility criteria for 12th marks where as most of the good engineering college needs atleast 75%. To get best college possible try to give some state colleges entrance exams also. State level college have less 12th marks eligibility criteria. Tell us about your location so that we can recommend good colleges in your region in which you are eligible.

I hope this answer will help, all the best for the future!!!