I made good money in my school and campus days buying and selling phones, bottled water, sweets, airtime and other stuff to corner shops/supermarkets. I was not the trading type and quite shy but I got better as I went along. You will learn good lessons from this. If you say you have some knowledge about building PCs then this is your skill, you could look at buying/selling new/used PC parts. You could charge for fitment too. Lots of people dont have these skills, yes their are many people doing this but does not mean you can't make money. These are short term goals but, you will need to know what you want to do long term and go for it.
Dont let anyone deter you. When I was in campus, over 1 December period I made R30,000. This enabled me to buy my first car cash for R60k, a black Polo Playa 1.6. Damn I miss that car.