Is it permissible for me to take an item worth 100 Riyals from the shop—knowing that they did not return my money or give me a replacement item after a defect was discovered in my first item—whether with or without the knowledge of the shop owner?

What you called a defect in the computer part is not a defect that warrants returning the sale, because it does not prevent the device from performing its function. Rather, it is a minor defect for which the sale is not annulled, as stated in Kashshaf al-Qina': "Nor is the sale annulled for a minor defect." Therefore, you are not entitled to compel the seller to accept the returned item, let alone assault his shop and take something from it. However, if he agrees to it, then it is good, for the hadith: "Whoever relieves a Muslim of his difficulty, Allah will relieve him of his difficulty."