I am sorry to say but you are not eligible for IIT JEE,ISEET on the basis of your Diploma course in Mechanical Engineering,because the basic eligibility condition for these Entrance Test is that you must have completed your 12th with Physics,Chemistry and Maths as core subjects,if you have completed your 12Th with these then you are eligible,but if you have completed only Diploma after 10Th,then you are not eligible for the Test.But you need to worry,here I am providing you the names of the Engineering Colleges which offers Engineering admissions for Diploma holders:
Thapar Institute of Engineering and Technology,Patiala.
Guru Gobind Singh IP University,Delhi.
Sant Longoval Institute of Engineering and Technology,Sangrur.
Harcourt Butler Technological Institute,Kanpur.
Punjab Technical University,Jallandhar.
Guru Tegh Bahadur Institute of Technology,Delhi
Amity School of Engineering and Technology,Noida
Delhi Technological University,Delhi.
Netaji Subhash Institute of Technology,Delhi.
Guru Nanak Dev Engineering College,Ludhiana
DAV Institute of Engineering and Technology,Jallandhar.
SBS College of Engineering and Technology,Ferozepur.
Chandigarh Group of Colleges,Chandigarh.
All the best.