Praise be to Allah.
If you cheated in the exams, and were among the top students and were given a prize for that, then this prize is not permissible for you, and you must return it to the body that awarded it, or return its value if time has passed and the computer is no longer functioning. That is because it is a prize that was given on condition that you were one of the top students – in a real sense, not by cheating – and that was not so in your case, so you are not entitled to it.
You do not have to inform the awarding body of that; rather it is sufficient for you to put this money in their account, or give it to them, even in the form of a donation.
If returning it is not possible, then give the money to be spent on similar activities as those undertaken by the awarding body, such as government departments responsible for education and schools, and the like. So you can buy a computer and give it to a school, and thus you will have done what is required of you.
This prize is not permissible for you, even if all the students cheated, because if they did that, it is not permissible for any of them to take a prize.
In addition to that, you must repent from having cheated, because cheating is a major sin, as the Prophet (blessings and peace of Allah be upon him) said “Whoever deceives (people) does not belong to me.” Narrated by Muslim (102).
For more information, please see the answer to question no. 279129.
And Allah knows best.