There are shops in Low Yat Plaza and nearby Imbi Plaza where you can sell your old machine. However, do not expect good pricing from them (usually cuthroat offers).

Please stick to one topic/thread on that subject. You already have an existing topic/thread here: Computers -> Hardware -> Hardware Questions & Answers -> How much could i sell this used desktop for?, 1 and half years old customized desktop. Also do not create multiple duplicate topics of the same subject all over the forum, otherwise that would be considered spamming. As for the pricing, its best to survey the Garage sales section and decide on the price that you want to sell...